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 $229.56   13.775%   $261.1819   $261.18   $261.20   $261.20  
  Purchase #2 $243.82   11.431%   $271.6911   $271.69   $271.70   $271.70  
  Purchase #3 $96.43   12.197%   $108.1916   $108.19   $108.20   $108.20  
  Purchase #4 $235.28   4.759%   $246.477   $246.48   $246.50   $246.50  
  Purchase #5 $197.93   3.342%   $204.5448   $204.54   $204.55   $204.50  
  Purchase #6 $227.67   12.679%   $256.5363   $256.54   $256.55   $256.50  
  Purchase #7 $18.59   5.216%   $19.5597   $19.56   $19.55   $19.60  
  7 purchase totals = $1,249.28       $1,368.1824   $1,368.18   $1,368.25   $1,368.20