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 $87.68   5.823%   $92.7856   $92.79   $92.80   $92.80  
  Purchase #2 $162.39   7.754%   $174.9817   $174.98   $175.00   $175.00  
  Purchase #3 $249.66   3.195%   $257.6366   $257.64   $257.65   $257.60  
  Purchase #4 $49.99   6.344%   $53.1614   $53.16   $53.15   $53.20  
  Purchase #5 $217.71   9.867%   $239.1914   $239.19   $239.20   $239.20  
  Purchase #6 $85.56   13.290%   $96.9309   $96.93   $96.95   $96.90  
  Purchase #7 $33.27   7.483%   $35.7596   $35.76   $35.75   $35.80  
  7 purchase totals = $886.26       $950.4472   $950.45   $950.50   $950.50