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 $156.73   13.405%   $177.7397   $177.74   $177.75   $177.70  
  Purchase #2 $234.30   12.227%   $262.9479   $262.95   $262.95   $262.90  
  Purchase #3 $29.51   5.398%   $31.1029   $31.10   $31.10   $31.10  
  Purchase #4 $10.92   12.282%   $12.2612   $12.26   $12.25   $12.30  
  Purchase #5 $177.88   5.448%   $187.5709   $187.57   $187.55   $187.60  
  Purchase #6 $62.30   9.180%   $68.0191   $68.02   $68.00   $68.00  
  Purchase #7 $209.82   9.766%   $230.311   $230.31   $230.30   $230.30  
  7 purchase totals = $881.46       $969.9527   $969.95   $969.90   $969.90