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 $196.65   6.715%   $209.855   $209.86   $209.85   $209.90  
  Purchase #2 $69.55   7.483%   $74.7544   $74.75   $74.75   $74.80  
  Purchase #3 $90.47   13.483%   $102.6681   $102.67   $102.65   $102.70  
  Purchase #4 $148.79   6.239%   $158.073   $158.07   $158.05   $158.10  
  Purchase #5 $237.57   12.120%   $266.3635   $266.36   $266.35   $266.40  
  Purchase #6 $106.79   10.623%   $118.1343   $118.13   $118.15   $118.10  
  Purchase #7 $224.45   4.708%   $235.0171   $235.02   $235.00   $235.00  
  7 purchase totals = $1,074.27       $1,164.8654   $1,164.86   $1,164.80   $1,165.00