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 $26.67   9.635%   $29.2397   $29.24   $29.25   $29.20  
  Purchase #2 $215.91   13.460%   $244.9715   $244.97   $244.95   $245.00  
  Purchase #3 $87.91   6.774%   $93.865   $93.87   $93.85   $93.90  
  Purchase #4 $154.36   10.180%   $170.0738   $170.07   $170.05   $170.10  
  Purchase #5 $102.57   13.269%   $116.18   $116.18   $116.20   $116.20  
  Purchase #6 $237.90   8.372%   $257.817   $257.82   $257.80   $257.80  
  Purchase #7 $92.65   9.615%   $101.5583   $101.56   $101.55   $101.60  
  7 purchase totals = $917.97       $1,013.7053   $1,013.71   $1,013.65   $1,013.80