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 $93.44   8.633%   $101.5067   $101.51   $101.50   $101.50  
  Purchase #2 $249.86   12.401%   $280.8451   $280.85   $280.85   $280.80  
  Purchase #3 $234.72   9.739%   $257.5794   $257.58   $257.60   $257.60  
  Purchase #4 $56.52   6.442%   $60.161   $60.16   $60.15   $60.20  
  Purchase #5 $135.76   13.795%   $154.4881   $154.49   $154.50   $154.50  
  Purchase #6 $149.76   9.867%   $164.5368   $164.54   $164.55   $164.50  
  Purchase #7 $75.64   9.503%   $82.8281   $82.83   $82.85   $82.80  
  7 purchase totals = $995.70       $1,101.9452   $1,101.96   $1,102.00   $1,101.90