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 $59.71   13.856%   $67.9834   $67.98   $68.00   $68.00  
  Purchase #2 $7.63   3.208%   $7.8748   $7.87   $7.85   $7.90  
  Purchase #3 $194.83   12.444%   $219.0746   $219.07   $219.05   $219.10  
  Purchase #4 $237.41   7.539%   $255.3083   $255.31   $255.30   $255.30  
  Purchase #5 $96.51   11.217%   $107.3355   $107.34   $107.35   $107.30  
  Purchase #6 $236.76   4.521%   $247.4639   $247.46   $247.45   $247.50  
  Purchase #7 $178.51   5.714%   $188.7101   $188.71   $188.70   $188.70  
  7 purchase totals = $1,011.36       $1,093.7506   $1,093.74   $1,093.70   $1,093.80