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 $194.60   4.792%   $203.9252   $203.93   $203.95   $203.90  
  Purchase #2 $247.51   8.321%   $268.1053   $268.11   $268.10   $268.10  
  Purchase #3 $154.94   13.325%   $175.5858   $175.59   $175.60   $175.60  
  Purchase #4 $220.41   5.385%   $232.2791   $232.28   $232.30   $232.30  
  Purchase #5 $237.85   11.482%   $265.1599   $265.16   $265.15   $265.20  
  Purchase #6 $64.82   3.713%   $67.2268   $67.23   $67.25   $67.20  
  Purchase #7 $153.87   6.774%   $164.2932   $164.29   $164.30   $164.30  
  7 purchase totals = $1,274.00       $1,376.5753   $1,376.59   $1,376.65   $1,376.60