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 $230.35   13.718%   $261.9494   $261.95   $261.95   $261.90  
  Purchase #2 $194.72   4.224%   $202.945   $202.95   $202.95   $202.90  
  Purchase #3 $96.64   6.587%   $103.0057   $103.01   $103.00   $103.00  
  Purchase #4 $157.93   3.164%   $162.9269   $162.93   $162.95   $162.90  
  Purchase #5 $167.70   12.568%   $188.7765   $188.78   $188.80   $188.80  
  Purchase #6 $133.57   7.795%   $143.9818   $143.98   $144.00   $144.00  
  Purchase #7 $247.27   10.163%   $272.4001   $272.40   $272.40   $272.40  
  7 purchase totals = $1,228.18       $1,335.9854   $1,336.00   $1,336.05   $1,335.90