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 $111.69   6.751%   $119.2302   $119.23   $119.25   $119.20  
  Purchase #2 $167.25   3.270%   $172.7191   $172.72   $172.70   $172.70  
  Purchase #3 $132.50   4.500%   $138.4625   $138.46   $138.45   $138.50  
  Purchase #4 $15.42   6.149%   $16.3682   $16.37   $16.35   $16.40  
  Purchase #5 $217.80   9.157%   $237.7439   $237.74   $237.75   $237.70  
  Purchase #6 $83.50   6.455%   $88.8899   $88.89   $88.90   $88.90  
  Purchase #7 $224.87   11.635%   $251.0336   $251.03   $251.05   $251.00  
  7 purchase totals = $953.03       $1,024.4474   $1,024.44   $1,024.45   $1,024.40