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 $34.91   5.303%   $36.7613   $36.76   $36.75   $36.80  
  Purchase #2 $182.43   13.817%   $207.6364   $207.64   $207.65   $207.60  
  Purchase #3 $113.49   12.374%   $127.5333   $127.53   $127.55   $127.50  
  Purchase #4 $93.57   11.636%   $104.4578   $104.46   $104.45   $104.50  
  Purchase #5 $188.75   9.787%   $207.223   $207.22   $207.20   $207.20  
  Purchase #6 $37.68   13.742%   $42.858   $42.86   $42.85   $42.90  
  Purchase #7 $108.80   5.377%   $114.6502   $114.65   $114.65   $114.70  
  7 purchase totals = $759.63       $841.1200   $841.12   $841.10   $841.20