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 $119.75   11.778%   $133.8542   $133.85   $133.85   $133.90  
  Purchase #2 $192.73   8.482%   $209.0774   $209.08   $209.10   $209.10  
  Purchase #3 $243.76   13.832%   $277.4769   $277.48   $277.50   $277.50  
  Purchase #4 $66.94   9.424%   $73.2484   $73.25   $73.25   $73.20  
  Purchase #5 $33.59   6.615%   $35.812   $35.81   $35.80   $35.80  
  Purchase #6 $169.49   8.211%   $183.4068   $183.41   $183.40   $183.40  
  Purchase #7 $247.88   5.288%   $260.9879   $260.99   $261.00   $261.00  
  7 purchase totals = $1,074.14       $1,173.8636   $1,173.87   $1,173.90   $1,173.90