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 $244.58   13.137%   $276.7105   $276.71   $276.70   $276.70  
  Purchase #2 $27.83   5.151%   $29.2635   $29.26   $29.25   $29.30  
  Purchase #3 $57.62   3.295%   $59.5186   $59.52   $59.50   $59.50  
  Purchase #4 $96.93   4.449%   $101.2424   $101.24   $101.25   $101.20  
  Purchase #5 $247.79   10.459%   $273.7064   $273.71   $273.70   $273.70  
  Purchase #6 $61.51   6.833%   $65.713   $65.71   $65.70   $65.70  
  Purchase #7 $57.77   9.603%   $63.3177   $63.32   $63.30   $63.30  
  7 purchase totals = $794.03       $869.4721   $869.47   $869.40   $869.40