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 $59.56   13.681%   $67.7084   $67.71   $67.70   $67.70  
  Purchase #2 $21.32   5.348%   $22.4602   $22.46   $22.45   $22.50  
  Purchase #3 $54.41   3.122%   $56.1087   $56.11   $56.10   $56.10  
  Purchase #4 $49.62   7.239%   $53.212   $53.21   $53.20   $53.20  
  Purchase #5 $236.41   5.679%   $249.8357   $249.84   $249.85   $249.80  
  Purchase #6 $95.91   13.483%   $108.8415   $108.84   $108.85   $108.80  
  Purchase #7 $59.95   13.446%   $68.0109   $68.01   $68.00   $68.00  
  7 purchase totals = $577.18       $626.1774   $626.18   $626.15   $626.10