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 $55.38   3.737%   $57.4496   $57.45   $57.45   $57.40  
  Purchase #2 $186.30   8.781%   $202.659   $202.66   $202.65   $202.70  
  Purchase #3 $247.93   9.648%   $271.8503   $271.85   $271.85   $271.90  
  Purchase #4 $116.72   9.390%   $127.68   $127.68   $127.70   $127.70  
  Purchase #5 $24.74   12.765%   $27.8981   $27.90   $27.90   $27.90  
  Purchase #6 $97.47   13.471%   $110.6002   $110.60   $110.60   $110.60  
  Purchase #7 $217.71   3.107%   $224.4742   $224.47   $224.45   $224.50  
  7 purchase totals = $946.25       $1,022.6114   $1,022.61   $1,022.60   $1,022.70