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 $195.83   4.673%   $204.9811   $204.98   $205.00   $205.00  
  Purchase #2 $60.73   13.756%   $69.084   $69.08   $69.10   $69.10  
  Purchase #3 $55.55   11.369%   $61.8655   $61.87   $61.85   $61.90  
  Purchase #4 $60.68   5.161%   $63.8117   $63.81   $63.80   $63.80  
  Purchase #5 $154.61   4.707%   $161.8875   $161.89   $161.90   $161.90  
  Purchase #6 $242.88   13.626%   $275.9748   $275.97   $275.95   $276.00  
  Purchase #7 $65.33   6.263%   $69.4216   $69.42   $69.40   $69.40  
  7 purchase totals = $835.61       $907.0262   $907.02   $907.00   $907.10