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 $66.63   9.761%   $73.1338   $73.13   $73.15   $73.10  
  Purchase #2 $53.37   10.524%   $58.9867   $58.99   $59.00   $59.00  
  Purchase #3 $168.27   8.158%   $181.9975   $182.00   $182.00   $182.00  
  Purchase #4 $246.95   13.281%   $279.7474   $279.75   $279.75   $279.70  
  Purchase #5 $246.64   5.726%   $260.7626   $260.76   $260.75   $260.80  
  Purchase #6 $152.70   3.865%   $158.6019   $158.60   $158.60   $158.60  
  Purchase #7 $39.85   3.758%   $41.3476   $41.35   $41.35   $41.30  
  7 purchase totals = $974.41       $1,054.5775   $1,054.58   $1,054.60   $1,054.50