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 $22.78   4.125%   $23.7197   $23.72   $23.70   $23.70  
  Purchase #2 $98.38   3.530%   $101.8528   $101.85   $101.85   $101.90  
  Purchase #3 $36.46   9.310%   $39.8544   $39.85   $39.85   $39.90  
  Purchase #4 $180.50   13.473%   $204.8188   $204.82   $204.80   $204.80  
  Purchase #5 $63.28   13.722%   $71.9633   $71.96   $71.95   $72.00  
  Purchase #6 $12.80   5.329%   $13.4821   $13.48   $13.50   $13.50  
  Purchase #7 $190.84   6.859%   $203.9297   $203.93   $203.95   $203.90  
  7 purchase totals = $605.04       $659.6208   $659.61   $659.60   $659.70