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 $180.97   12.738%   $204.022   $204.02   $204.00   $204.00  
  Purchase #2 $98.80   11.353%   $110.0168   $110.02   $110.00   $110.00  
  Purchase #3 $43.92   6.195%   $46.6408   $46.64   $46.65   $46.60  
  Purchase #4 $69.38   10.572%   $76.7149   $76.71   $76.70   $76.70  
  Purchase #5 $12.41   9.820%   $13.6287   $13.63   $13.65   $13.60  
  Purchase #6 $88.86   8.690%   $96.5819   $96.58   $96.60   $96.60  
  Purchase #7 $210.25   9.315%   $229.8348   $229.83   $229.85   $229.80  
  7 purchase totals = $704.59       $777.4399   $777.43   $777.45   $777.30