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 $223.76   9.717%   $245.5028   $245.50   $245.50   $245.50  
  Purchase #2 $159.49   12.649%   $179.6639   $179.66   $179.65   $179.70  
  Purchase #3 $36.63   7.252%   $39.2864   $39.29   $39.30   $39.30  
  Purchase #4 $85.94   12.633%   $96.7968   $96.80   $96.80   $96.80  
  Purchase #5 $55.26   11.276%   $61.4911   $61.49   $61.50   $61.50  
  Purchase #6 $174.97   8.306%   $189.503   $189.50   $189.50   $189.50  
  Purchase #7 $60.32   7.302%   $64.7246   $64.72   $64.70   $64.70  
  7 purchase totals = $796.37       $876.9686   $876.96   $876.95   $877.00