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 $119.73   13.342%   $135.7044   $135.70   $135.70   $135.70  
  Purchase #2 $197.83   9.610%   $216.8415   $216.84   $216.85   $216.80  
  Purchase #3 $151.85   5.622%   $160.387   $160.39   $160.40   $160.40  
  Purchase #4 $57.60   11.807%   $64.4008   $64.40   $64.40   $64.40  
  Purchase #5 $25.52   4.581%   $26.6891   $26.69   $26.70   $26.70  
  Purchase #6 $136.38   8.373%   $147.7991   $147.80   $147.80   $147.80  
  Purchase #7 $179.45   6.386%   $190.9097   $190.91   $190.90   $190.90  
  7 purchase totals = $868.36       $942.7316   $942.73   $942.75   $942.70