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 $204.94   12.204%   $229.9509   $229.95   $229.95   $230.00  
  Purchase #2 $57.84   7.523%   $62.1913   $62.19   $62.20   $62.20  
  Purchase #3 $63.43   5.266%   $66.7702   $66.77   $66.75   $66.80  
  Purchase #4 $145.82   13.866%   $166.0394   $166.04   $166.05   $166.00  
  Purchase #5 $247.43   6.657%   $263.9014   $263.90   $263.90   $263.90  
  Purchase #6 $5.45   8.562%   $5.9166   $5.92   $5.90   $5.90  
  Purchase #7 $193.43   9.408%   $211.6279   $211.63   $211.65   $211.60  
  7 purchase totals = $918.34       $1,006.3977   $1,006.40   $1,006.40   $1,006.40