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 $191.74   3.411%   $198.2803   $198.28   $198.30   $198.30  
  Purchase #2 $128.55   9.733%   $141.0618   $141.06   $141.05   $141.10  
  Purchase #3 $182.79   3.352%   $188.9171   $188.92   $188.90   $188.90  
  Purchase #4 $193.55   4.496%   $202.252   $202.25   $202.25   $202.30  
  Purchase #5 $19.76   9.208%   $21.5795   $21.58   $21.60   $21.60  
  Purchase #6 $130.52   6.657%   $139.2087   $139.21   $139.20   $139.20  
  Purchase #7 $140.39   11.502%   $156.5377   $156.54   $156.55   $156.50  
  7 purchase totals = $987.30       $1,047.8371   $1,047.84   $1,047.85   $1,047.90