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 $59.42   8.134%   $64.2532   $64.25   $64.25   $64.30  
  Purchase #2 $160.81   5.620%   $169.8475   $169.85   $169.85   $169.80  
  Purchase #3 $201.91   7.586%   $217.2269   $217.23   $217.25   $217.20  
  Purchase #4 $179.44   8.247%   $194.2384   $194.24   $194.25   $194.20  
  Purchase #5 $200.81   10.619%   $222.134   $222.13   $222.15   $222.10  
  Purchase #6 $185.64   9.416%   $203.1199   $203.12   $203.10   $203.10  
  Purchase #7 $167.79   9.168%   $183.173   $183.17   $183.15   $183.20  
  7 purchase totals = $1,155.82       $1,253.9929   $1,253.99   $1,254.00   $1,253.90