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 $79.94   11.645%   $89.249   $89.25   $89.25   $89.20  
  Purchase #2 $77.65   4.488%   $81.1349   $81.13   $81.15   $81.10  
  Purchase #3 $189.73   6.838%   $202.7037   $202.70   $202.70   $202.70  
  Purchase #4 $207.53   6.707%   $221.449   $221.45   $221.45   $221.40  
  Purchase #5 $217.78   10.468%   $240.5772   $240.58   $240.60   $240.60  
  Purchase #6 $245.64   3.543%   $254.343   $254.34   $254.35   $254.30  
  Purchase #7 $157.25   13.178%   $177.9724   $177.97   $177.95   $178.00  
  7 purchase totals = $1,175.52       $1,267.4292   $1,267.42   $1,267.45   $1,267.30