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 $44.83   13.402%   $50.8381   $50.84   $50.85   $50.80  
  Purchase #2 $67.88   10.287%   $74.8628   $74.86   $74.85   $74.90  
  Purchase #3 $193.37   8.842%   $210.4678   $210.47   $210.45   $210.50  
  Purchase #4 $202.64   5.422%   $213.6271   $213.63   $213.65   $213.60  
  Purchase #5 $140.25   11.872%   $156.9005   $156.90   $156.90   $156.90  
  Purchase #6 $235.74   11.287%   $262.348   $262.35   $262.35   $262.30  
  Purchase #7 $93.26   6.708%   $99.5159   $99.52   $99.50   $99.50  
  7 purchase totals = $977.97       $1,068.5602   $1,068.57   $1,068.55   $1,068.50