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 $152.58   9.349%   $166.8447   $166.84   $166.85   $166.80  
  Purchase #2 $59.64   8.851%   $64.9187   $64.92   $64.90   $64.90  
  Purchase #3 $16.68   4.119%   $17.367   $17.37   $17.35   $17.40  
  Purchase #4 $232.72   9.552%   $254.9494   $254.95   $254.95   $254.90  
  Purchase #5 $141.25   7.290%   $151.5471   $151.55   $151.55   $151.50  
  Purchase #6 $63.92   12.546%   $71.9394   $71.94   $71.95   $71.90  
  Purchase #7 $224.67   4.497%   $234.7734   $234.77   $234.75   $234.80  
  7 purchase totals = $891.46       $962.3397   $962.34   $962.30   $962.20