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 $235.76   10.572%   $260.6845   $260.68   $260.70   $260.70  
  Purchase #2 $129.76   3.319%   $134.0667   $134.07   $134.05   $134.10  
  Purchase #3 $195.96   5.616%   $206.9651   $206.97   $206.95   $207.00  
  Purchase #4 $53.63   10.114%   $59.0541   $59.05   $59.05   $59.10  
  Purchase #5 $161.99   6.539%   $172.5825   $172.58   $172.60   $172.60  
  Purchase #6 $130.48   3.499%   $135.0455   $135.05   $135.05   $135.00  
  Purchase #7 $128.79   11.767%   $143.9447   $143.94   $143.95   $143.90  
  7 purchase totals = $1,036.37       $1,112.3431   $1,112.34   $1,112.35   $1,112.40