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 $11.42   11.457%   $12.7284   $12.73   $12.75   $12.70  
  Purchase #2 $235.30   11.281%   $261.8442   $261.84   $261.85   $261.80  
  Purchase #3 $154.61   12.218%   $173.5002   $173.50   $173.50   $173.50  
  Purchase #4 $235.94   12.351%   $265.0809   $265.08   $265.10   $265.10  
  Purchase #5 $212.72   12.710%   $239.7567   $239.76   $239.75   $239.80  
  Purchase #6 $70.94   3.698%   $73.5634   $73.56   $73.55   $73.60  
  Purchase #7 $37.86   5.829%   $40.0669   $40.07   $40.05   $40.10  
  7 purchase totals = $958.79       $1,066.5407   $1,066.54   $1,066.55   $1,066.60