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 $123.57   7.852%   $133.2727   $133.27   $133.25   $133.30  
  Purchase #2 $230.48   9.216%   $251.721   $251.72   $251.70   $251.70  
  Purchase #3 $141.99   9.398%   $155.3342   $155.33   $155.35   $155.30  
  Purchase #4 $12.78   8.578%   $13.8763   $13.88   $13.90   $13.90  
  Purchase #5 $167.45   6.144%   $177.7381   $177.74   $177.75   $177.70  
  Purchase #6 $131.57   7.142%   $140.9667   $140.97   $140.95   $141.00  
  Purchase #7 $163.43   11.741%   $182.6183   $182.62   $182.60   $182.60  
  7 purchase totals = $971.27       $1,055.5273   $1,055.53   $1,055.50   $1,055.50