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 $246.68   8.702%   $268.1461   $268.15   $268.15   $268.10  
  Purchase #2 $172.77   6.725%   $184.3888   $184.39   $184.40   $184.40  
  Purchase #3 $96.35   5.596%   $101.7417   $101.74   $101.75   $101.70  
  Purchase #4 $110.27   13.356%   $124.9977   $125.00   $125.00   $125.00  
  Purchase #5 $26.64   3.792%   $27.6502   $27.65   $27.65   $27.70  
  Purchase #6 $171.41   13.843%   $195.1383   $195.14   $195.15   $195.10  
  Purchase #7 $124.93   7.537%   $134.346   $134.35   $134.35   $134.30  
  7 purchase totals = $949.05       $1,036.4088   $1,036.42   $1,036.45   $1,036.30