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 $58.93   10.370%   $65.041   $65.04   $65.05   $65.00  
  Purchase #2 $118.99   7.776%   $128.2427   $128.24   $128.25   $128.20  
  Purchase #3 $55.91   6.845%   $59.737   $59.74   $59.75   $59.70  
  Purchase #4 $203.74   4.204%   $212.3052   $212.31   $212.30   $212.30  
  Purchase #5 $246.99   6.565%   $263.2049   $263.20   $263.20   $263.20  
  Purchase #6 $126.56   8.750%   $137.634   $137.63   $137.65   $137.60  
  Purchase #7 $123.29   7.119%   $132.067   $132.07   $132.05   $132.10  
  7 purchase totals = $934.41       $998.2318   $998.23   $998.25   $998.10