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 $189.96   6.363%   $202.0472   $202.05   $202.05   $202.00  
  Purchase #2 $101.71   6.179%   $107.9947   $107.99   $108.00   $108.00  
  Purchase #3 $69.69   3.814%   $72.348   $72.35   $72.35   $72.30  
  Purchase #4 $148.43   4.195%   $154.6566   $154.66   $154.65   $154.70  
  Purchase #5 $103.51   7.682%   $111.4616   $111.46   $111.45   $111.50  
  Purchase #6 $89.66   8.871%   $97.6137   $97.61   $97.60   $97.60  
  Purchase #7 $150.99   8.368%   $163.6248   $163.62   $163.60   $163.60  
  7 purchase totals = $853.95       $909.7466   $909.74   $909.70   $909.70