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 $19.36   5.297%   $20.3855   $20.39   $20.40   $20.40  
  Purchase #2 $21.93   9.806%   $24.0805   $24.08   $24.10   $24.10  
  Purchase #3 $41.47   11.133%   $46.0869   $46.09   $46.10   $46.10  
  Purchase #4 $10.31   3.422%   $10.6628   $10.66   $10.65   $10.70  
  Purchase #5 $175.48   11.362%   $195.418   $195.42   $195.40   $195.40  
  Purchase #6 $199.61   3.733%   $207.0614   $207.06   $207.05   $207.10  
  Purchase #7 $97.36   12.382%   $109.4151   $109.42   $109.40   $109.40  
  7 purchase totals = $565.52       $613.1102   $613.12   $613.10   $613.20