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 $29.57   13.781%   $33.645   $33.65   $33.65   $33.60  
  Purchase #2 $241.45   6.685%   $257.5909   $257.59   $257.60   $257.60  
  Purchase #3 $118.76   4.742%   $124.3916   $124.39   $124.40   $124.40  
  Purchase #4 $23.60   9.796%   $25.9119   $25.91   $25.90   $25.90  
  Purchase #5 $179.85   5.538%   $189.8101   $189.81   $189.80   $189.80  
  Purchase #6 $128.98   3.685%   $133.7329   $133.73   $133.75   $133.70  
  Purchase #7 $75.81   13.776%   $86.2536   $86.25   $86.25   $86.30  
  7 purchase totals = $798.02       $851.3360   $851.33   $851.35   $851.30