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 $64.67   8.126%   $69.9251   $69.93   $69.95   $69.90  
  Purchase #2 $19.65   10.327%   $21.6793   $21.68   $21.70   $21.70  
  Purchase #3 $73.33   3.515%   $75.9075   $75.91   $75.90   $75.90  
  Purchase #4 $59.27   3.331%   $61.2443   $61.24   $61.25   $61.20  
  Purchase #5 $65.72   8.206%   $71.113   $71.11   $71.10   $71.10  
  Purchase #6 $113.92   10.610%   $126.0069   $126.01   $126.00   $126.00  
  Purchase #7 $192.41   5.305%   $202.6174   $202.62   $202.60   $202.60  
  7 purchase totals = $588.97       $628.4935   $628.50   $628.50   $628.40