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 $139.59   10.847%   $154.7313   $154.73   $154.75   $154.70  
  Purchase #2 $235.85   13.264%   $267.1331   $267.13   $267.15   $267.10  
  Purchase #3 $154.63   10.449%   $170.7873   $170.79   $170.80   $170.80  
  Purchase #4 $59.99   8.799%   $65.2685   $65.27   $65.25   $65.30  
  Purchase #5 $35.54   3.130%   $36.6524   $36.65   $36.65   $36.70  
  Purchase #6 $250.40   10.427%   $276.5092   $276.51   $276.50   $276.50  
  Purchase #7 $187.25   12.364%   $210.4016   $210.40   $210.40   $210.40  
  7 purchase totals = $1,063.25       $1,181.4834   $1,181.48   $1,181.50   $1,181.50