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 $20.43   7.533%   $21.969   $21.97   $21.95   $22.00  
  Purchase #2 $189.38   12.516%   $213.0828   $213.08   $213.10   $213.10  
  Purchase #3 $185.42   4.488%   $193.7416   $193.74   $193.75   $193.70  
  Purchase #4 $102.41   13.759%   $116.5006   $116.50   $116.50   $116.50  
  Purchase #5 $99.76   10.462%   $110.1969   $110.20   $110.20   $110.20  
  Purchase #6 $200.39   8.815%   $218.0544   $218.05   $218.05   $218.10  
  Purchase #7 $209.39   5.669%   $221.2603   $221.26   $221.25   $221.30  
  7 purchase totals = $1,007.18       $1,094.8056   $1,094.80   $1,094.80   $1,094.90