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 $83.89   10.532%   $92.7253   $92.73   $92.75   $92.70  
  Purchase #2 $31.49   8.417%   $34.1405   $34.14   $34.15   $34.10  
  Purchase #3 $69.92   8.386%   $75.7835   $75.78   $75.80   $75.80  
  Purchase #4 $244.94   10.742%   $271.2515   $271.25   $271.25   $271.30  
  Purchase #5 $169.94   7.220%   $182.2097   $182.21   $182.20   $182.20  
  Purchase #6 $160.44   12.441%   $180.4003   $180.40   $180.40   $180.40  
  Purchase #7 $206.32   7.825%   $222.4645   $222.46   $222.45   $222.50  
  7 purchase totals = $966.94       $1,058.9753   $1,058.97   $1,059.00   $1,059.00