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 $198.56   9.620%   $217.6615   $217.66   $217.65   $217.70  
  Purchase #2 $59.65   4.108%   $62.1004   $62.10   $62.10   $62.10  
  Purchase #3 $246.49   11.754%   $275.4624   $275.46   $275.45   $275.50  
  Purchase #4 $59.28   8.113%   $64.0894   $64.09   $64.10   $64.10  
  Purchase #5 $47.25   7.604%   $50.8429   $50.84   $50.85   $50.80  
  Purchase #6 $229.65   7.687%   $247.3032   $247.30   $247.30   $247.30  
  Purchase #7 $100.75   9.337%   $110.157   $110.16   $110.15   $110.20  
  7 purchase totals = $941.63       $1,027.6168   $1,027.61   $1,027.60   $1,027.70