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 $186.31   12.343%   $209.3062   $209.31   $209.30   $209.30  
  Purchase #2 $233.46   10.405%   $257.7515   $257.75   $257.75   $257.80  
  Purchase #3 $114.83   4.758%   $120.2936   $120.29   $120.30   $120.30  
  Purchase #4 $95.92   4.733%   $100.4599   $100.46   $100.45   $100.50  
  Purchase #5 $175.82   9.562%   $192.6319   $192.63   $192.65   $192.60  
  Purchase #6 $200.94   8.155%   $217.3267   $217.33   $217.35   $217.30  
  Purchase #7 $150.77   13.363%   $170.9174   $170.92   $170.90   $170.90  
  7 purchase totals = $1,158.05       $1,268.6872   $1,268.69   $1,268.70   $1,268.70