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 $46.58   11.687%   $52.0238   $52.02   $52.00   $52.00  
  Purchase #2 $22.82   13.861%   $25.9831   $25.98   $26.00   $26.00  
  Purchase #3 $154.38   4.555%   $161.412   $161.41   $161.40   $161.40  
  Purchase #4 $199.66   4.618%   $208.8803   $208.88   $208.90   $208.90  
  Purchase #5 $39.56   4.627%   $41.3904   $41.39   $41.40   $41.40  
  Purchase #6 $78.29   5.182%   $82.347   $82.35   $82.35   $82.30  
  Purchase #7 $204.80   9.830%   $224.9318   $224.93   $224.95   $224.90  
  7 purchase totals = $746.09       $796.9684   $796.96   $797.00   $796.90