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 $61.49   7.300%   $65.9788   $65.98   $66.00   $66.00  
  Purchase #2 $211.70   11.245%   $235.5057   $235.51   $235.50   $235.50  
  Purchase #3 $126.86   3.249%   $130.9817   $130.98   $131.00   $131.00  
  Purchase #4 $247.88   11.857%   $277.2711   $277.27   $277.25   $277.30  
  Purchase #5 $205.28   10.239%   $226.2986   $226.30   $226.30   $226.30  
  Purchase #6 $112.97   8.692%   $122.7894   $122.79   $122.80   $122.80  
  Purchase #7 $14.32   3.856%   $14.8722   $14.87   $14.85   $14.90  
  7 purchase totals = $980.50       $1,073.6975   $1,073.70   $1,073.70   $1,073.80