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 $157.37   12.837%   $177.5716   $177.57   $177.55   $177.60  
  Purchase #2 $149.97   4.593%   $156.8581   $156.86   $156.85   $156.90  
  Purchase #3 $13.56   6.637%   $14.46   $14.46   $14.45   $14.50  
  Purchase #4 $71.99   13.702%   $81.8541   $81.85   $81.85   $81.90  
  Purchase #5 $85.34   11.503%   $95.1567   $95.16   $95.15   $95.20  
  Purchase #6 $232.77   12.235%   $261.2494   $261.25   $261.25   $261.20  
  Purchase #7 $243.31   4.403%   $254.0229   $254.02   $254.00   $254.00  
  7 purchase totals = $954.31       $1,041.1728   $1,041.17   $1,041.10   $1,041.30