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 $221.71   6.308%   $235.6955   $235.70   $235.70   $235.70  
  Purchase #2 $183.66   3.860%   $190.7493   $190.75   $190.75   $190.70  
  Purchase #3 $33.27   4.143%   $34.6484   $34.65   $34.65   $34.60  
  Purchase #4 $98.56   12.515%   $110.8948   $110.89   $110.90   $110.90  
  Purchase #5 $26.98   10.863%   $29.9108   $29.91   $29.90   $29.90  
  Purchase #6 $150.38   6.862%   $160.6991   $160.70   $160.70   $160.70  
  Purchase #7 $247.41   10.432%   $273.2198   $273.22   $273.20   $273.20  
  7 purchase totals = $961.97       $1,035.8177   $1,035.82   $1,035.80   $1,035.70