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 $158.98   12.603%   $179.0162   $179.02   $179.00   $179.00  
  Purchase #2 $75.49   12.754%   $85.118   $85.12   $85.10   $85.10  
  Purchase #3 $225.41   6.556%   $240.1879   $240.19   $240.20   $240.20  
  Purchase #4 $233.54   6.621%   $249.0027   $249.00   $249.00   $249.00  
  Purchase #5 $95.77   11.144%   $106.4426   $106.44   $106.45   $106.40  
  Purchase #6 $136.55   10.859%   $151.378   $151.38   $151.40   $151.40  
  Purchase #7 $247.43   9.797%   $271.6707   $271.67   $271.65   $271.70  
  7 purchase totals = $1,173.17       $1,282.8161   $1,282.82   $1,282.80   $1,282.80