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 $209.42   7.290%   $224.6867   $224.69   $224.70   $224.70  
  Purchase #2 $8.43   5.175%   $8.8663   $8.87   $8.85   $8.90  
  Purchase #3 $83.68   11.738%   $93.5024   $93.50   $93.50   $93.50  
  Purchase #4 $110.32   9.364%   $120.6504   $120.65   $120.65   $120.70  
  Purchase #5 $86.53   4.748%   $90.6384   $90.64   $90.65   $90.60  
  Purchase #6 $245.81   4.380%   $256.5765   $256.58   $256.60   $256.60  
  Purchase #7 $248.30   10.269%   $273.7979   $273.80   $273.80   $273.80  
  7 purchase totals = $992.49       $1,068.7186   $1,068.73   $1,068.75   $1,068.80