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 $68.79   10.464%   $75.9882   $75.99   $76.00   $76.00  
  Purchase #2 $10.96   7.833%   $11.8185   $11.82   $11.80   $11.80  
  Purchase #3 $37.78   12.809%   $42.6192   $42.62   $42.60   $42.60  
  Purchase #4 $236.81   4.359%   $247.1325   $247.13   $247.15   $247.10  
  Purchase #5 $177.28   7.604%   $190.7604   $190.76   $190.75   $190.80  
  Purchase #6 $77.48   8.330%   $83.9341   $83.93   $83.95   $83.90  
  Purchase #7 $96.98   13.608%   $110.177   $110.18   $110.20   $110.20  
  7 purchase totals = $706.08       $762.4299   $762.43   $762.45   $762.40