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 $23.59   12.699%   $26.5857   $26.59   $26.60   $26.60  
  Purchase #2 $237.34   9.520%   $259.9348   $259.93   $259.95   $259.90  
  Purchase #3 $11.73   6.320%   $12.4713   $12.47   $12.45   $12.50  
  Purchase #4 $113.55   6.679%   $121.134   $121.13   $121.15   $121.10  
  Purchase #5 $200.51   11.833%   $224.2363   $224.24   $224.25   $224.20  
  Purchase #6 $156.29   3.748%   $162.1477   $162.15   $162.15   $162.10  
  Purchase #7 $62.39   3.500%   $64.5737   $64.57   $64.55   $64.60  
  7 purchase totals = $805.40       $871.0835   $871.08   $871.10   $871.00