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 $48.63   4.487%   $50.812   $50.81   $50.80   $50.80  
  Purchase #2 $60.54   6.314%   $64.3625   $64.36   $64.35   $64.40  
  Purchase #3 $147.41   8.285%   $159.6229   $159.62   $159.60   $159.60  
  Purchase #4 $150.67   6.521%   $160.4952   $160.50   $160.50   $160.50  
  Purchase #5 $216.53   13.636%   $246.056   $246.06   $246.05   $246.10  
  Purchase #6 $247.54   7.213%   $265.3951   $265.40   $265.40   $265.40  
  Purchase #7 $86.63   6.868%   $92.5797   $92.58   $92.60   $92.60  
  7 purchase totals = $957.95       $1,039.3234   $1,039.33   $1,039.30   $1,039.40