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 $247.60   6.200%   $262.9512   $262.95   $262.95   $263.00  
  Purchase #2 $140.96   7.409%   $151.4037   $151.40   $151.40   $151.40  
  Purchase #3 $159.71   8.640%   $173.5089   $173.51   $173.50   $173.50  
  Purchase #4 $39.63   8.344%   $42.9367   $42.94   $42.95   $42.90  
  Purchase #5 $98.64   8.306%   $106.833   $106.83   $106.85   $106.80  
  Purchase #6 $57.75   13.622%   $65.6167   $65.62   $65.60   $65.60  
  Purchase #7 $226.97   7.822%   $244.7236   $244.72   $244.70   $244.70  
  7 purchase totals = $971.26       $1,047.9738   $1,047.97   $1,047.95   $1,047.90