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 $187.31   11.564%   $208.9705   $208.97   $208.95   $209.00  
  Purchase #2 $180.92   12.430%   $203.4084   $203.41   $203.40   $203.40  
  Purchase #3 $69.41   10.428%   $76.6481   $76.65   $76.65   $76.60  
  Purchase #4 $52.85   10.110%   $58.1931   $58.19   $58.20   $58.20  
  Purchase #5 $229.83   6.176%   $244.0243   $244.02   $244.00   $244.00  
  Purchase #6 $195.49   9.768%   $214.5855   $214.59   $214.60   $214.60  
  Purchase #7 $45.67   6.657%   $48.7103   $48.71   $48.70   $48.70  
  7 purchase totals = $961.48       $1,054.5402   $1,054.54   $1,054.50   $1,054.50