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 $85.78   10.266%   $94.5862   $94.59   $94.60   $94.60  
  Purchase #2 $191.51   3.380%   $197.983   $197.98   $198.00   $198.00  
  Purchase #3 $121.67   5.255%   $128.0638   $128.06   $128.05   $128.10  
  Purchase #4 $67.46   3.855%   $70.0606   $70.06   $70.05   $70.10  
  Purchase #5 $170.64   10.541%   $188.6272   $188.63   $188.65   $188.60  
  Purchase #6 $64.72   7.830%   $69.7876   $69.79   $69.80   $69.80  
  Purchase #7 $41.38   6.817%   $44.2009   $44.20   $44.20   $44.20  
  7 purchase totals = $743.16       $793.3093   $793.31   $793.35   $793.40