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 $117.53   12.325%   $132.0156   $132.02   $132.00   $132.00  
  Purchase #2 $60.96   6.592%   $64.9785   $64.98   $65.00   $65.00  
  Purchase #3 $242.92   9.164%   $265.1812   $265.18   $265.20   $265.20  
  Purchase #4 $153.39   8.733%   $166.7855   $166.79   $166.80   $166.80  
  Purchase #5 $101.94   7.132%   $109.2104   $109.21   $109.20   $109.20  
  Purchase #6 $52.30   5.798%   $55.3324   $55.33   $55.35   $55.30  
  Purchase #7 $213.26   12.653%   $240.2438   $240.24   $240.25   $240.20  
  7 purchase totals = $942.30       $1,033.7474   $1,033.75   $1,033.80   $1,033.70