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 $234.26   4.447%   $244.6775   $244.68   $244.70   $244.70  
  Purchase #2 $200.51   13.235%   $227.0475   $227.05   $227.05   $227.00  
  Purchase #3 $25.47   3.822%   $26.4435   $26.44   $26.45   $26.40  
  Purchase #4 $226.69   11.765%   $253.3601   $253.36   $253.35   $253.40  
  Purchase #5 $246.98   3.112%   $254.666   $254.67   $254.65   $254.70  
  Purchase #6 $221.62   13.630%   $251.8268   $251.83   $251.85   $251.80  
  Purchase #7 $58.89   12.825%   $66.4426   $66.44   $66.45   $66.40  
  7 purchase totals = $1,214.42       $1,324.4640   $1,324.47   $1,324.50   $1,324.40