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 $54.36   12.198%   $60.9908   $60.99   $61.00   $61.00  
  Purchase #2 $149.45   11.532%   $166.6846   $166.68   $166.70   $166.70  
  Purchase #3 $128.89   12.159%   $144.5617   $144.56   $144.55   $144.60  
  Purchase #4 $61.91   3.847%   $64.2917   $64.29   $64.30   $64.30  
  Purchase #5 $218.86   12.174%   $245.504   $245.50   $245.50   $245.50  
  Purchase #6 $115.90   9.183%   $126.5431   $126.54   $126.55   $126.50  
  Purchase #7 $37.61   8.346%   $40.7489   $40.75   $40.75   $40.70  
  7 purchase totals = $766.98       $849.3248   $849.31   $849.35   $849.30