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 $87.45   10.571%   $96.6943   $96.69   $96.70   $96.70  
  Purchase #2 $189.48   7.594%   $203.8691   $203.87   $203.85   $203.90  
  Purchase #3 $55.38   12.823%   $62.4814   $62.48   $62.50   $62.50  
  Purchase #4 $122.74   10.146%   $135.1932   $135.19   $135.20   $135.20  
  Purchase #5 $121.92   12.317%   $136.9369   $136.94   $136.95   $136.90  
  Purchase #6 $177.56   5.480%   $187.2903   $187.29   $187.30   $187.30  
  Purchase #7 $250.80   13.783%   $285.3678   $285.37   $285.35   $285.40  
  7 purchase totals = $1,005.33       $1,107.8330   $1,107.83   $1,107.85   $1,107.90