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 $242.84   7.823%   $261.8374   $261.84   $261.85   $261.80  
  Purchase #2 $97.77   4.697%   $102.3623   $102.36   $102.35   $102.40  
  Purchase #3 $210.47   3.425%   $217.6786   $217.68   $217.70   $217.70  
  Purchase #4 $87.70   9.237%   $95.8008   $95.80   $95.80   $95.80  
  Purchase #5 $37.33   10.434%   $41.225   $41.23   $41.25   $41.20  
  Purchase #6 $203.85   3.341%   $210.6606   $210.66   $210.65   $210.70  
  Purchase #7 $85.75   11.547%   $95.6516   $95.65   $95.65   $95.70  
  7 purchase totals = $965.71       $1,025.2163   $1,025.22   $1,025.25   $1,025.30