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 $33.38   12.153%   $37.4367   $37.44   $37.45   $37.40  
  Purchase #2 $133.94   10.198%   $147.5992   $147.60   $147.60   $147.60  
  Purchase #3 $183.30   9.457%   $200.6347   $200.63   $200.65   $200.60  
  Purchase #4 $113.74   10.734%   $125.9489   $125.95   $125.95   $125.90  
  Purchase #5 $49.60   10.508%   $54.812   $54.81   $54.80   $54.80  
  Purchase #6 $11.94   9.295%   $13.0498   $13.05   $13.05   $13.00  
  Purchase #7 $153.38   9.863%   $168.5079   $168.51   $168.50   $168.50  
  7 purchase totals = $679.28       $747.9892   $747.99   $748.00   $747.80