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 $76.53   6.602%   $81.5825   $81.58   $81.60   $81.60  
  Purchase #2 $233.45   11.855%   $261.1255   $261.13   $261.15   $261.10  
  Purchase #3 $26.99   4.581%   $28.2264   $28.23   $28.25   $28.20  
  Purchase #4 $232.65   6.362%   $247.4512   $247.45   $247.45   $247.50  
  Purchase #5 $204.62   9.662%   $224.3904   $224.39   $224.40   $224.40  
  Purchase #6 $179.80   7.132%   $192.6233   $192.62   $192.60   $192.60  
  Purchase #7 $84.96   11.833%   $95.0133   $95.01   $95.00   $95.00  
  7 purchase totals = $1,039.00       $1,130.4126   $1,130.41   $1,130.45   $1,130.40