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 $203.98   3.137%   $210.3789   $210.38   $210.40   $210.40  
  Purchase #2 $241.79   11.325%   $269.1727   $269.17   $269.15   $269.20  
  Purchase #3 $111.63   13.262%   $126.4344   $126.43   $126.45   $126.40  
  Purchase #4 $161.65   4.756%   $169.3381   $169.34   $169.35   $169.30  
  Purchase #5 $54.68   10.635%   $60.4952   $60.50   $60.50   $60.50  
  Purchase #6 $206.32   9.352%   $225.615   $225.62   $225.60   $225.60  
  Purchase #7 $134.55   10.729%   $148.9859   $148.99   $149.00   $149.00  
  7 purchase totals = $1,114.60       $1,210.4202   $1,210.43   $1,210.45   $1,210.40