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 $112.99   5.746%   $119.4824   $119.48   $119.50   $119.50  
  Purchase #2 $191.40   4.133%   $199.3106   $199.31   $199.30   $199.30  
  Purchase #3 $46.27   10.479%   $51.1186   $51.12   $51.10   $51.10  
  Purchase #4 $194.70   4.756%   $203.9599   $203.96   $203.95   $204.00  
  Purchase #5 $215.60   9.651%   $236.4076   $236.41   $236.40   $236.40  
  Purchase #6 $165.38   11.191%   $183.8877   $183.89   $183.90   $183.90  
  Purchase #7 $21.67   7.379%   $23.269   $23.27   $23.25   $23.30  
  7 purchase totals = $948.01       $1,017.4358   $1,017.44   $1,017.40   $1,017.50