Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $114.61   7.752%   $123.4946   $123.49   $123.50   $123.50  
  Purchase #2 $181.26   11.192%   $201.5466   $201.55   $201.55   $201.50  
  Purchase #3 $247.68   12.159%   $277.7954   $277.80   $277.80   $277.80  
  Purchase #4 $107.26   8.591%   $116.4747   $116.47   $116.45   $116.50  
  Purchase #5 $152.29   10.120%   $167.7017   $167.70   $167.70   $167.70  
  Purchase #6 $132.83   3.631%   $137.6531   $137.65   $137.65   $137.70  
  Purchase #7 $229.81   6.477%   $244.6948   $244.69   $244.70   $244.70  
  7 purchase totals = $1,165.74       $1,269.3609   $1,269.35   $1,269.35   $1,269.40