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 $67.67   4.525%   $70.7321   $70.73   $70.75   $70.70  
  Purchase #2 $183.69   11.223%   $204.3055   $204.31   $204.30   $204.30  
  Purchase #3 $210.28   9.201%   $229.6279   $229.63   $229.65   $229.60  
  Purchase #4 $6.62   4.856%   $6.9415   $6.94   $6.95   $6.90  
  Purchase #5 $169.73   11.677%   $189.5494   $189.55   $189.55   $189.50  
  Purchase #6 $225.86   12.657%   $254.4471   $254.45   $254.45   $254.40  
  Purchase #7 $107.59   12.845%   $121.4099   $121.41   $121.40   $121.40  
  7 purchase totals = $971.44       $1,077.0134   $1,077.02   $1,077.05   $1,076.80