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 $231.85   6.821%   $247.6645   $247.66   $247.65   $247.70  
  Purchase #2 $95.79   7.776%   $103.2386   $103.24   $103.25   $103.20  
  Purchase #3 $204.27   4.739%   $213.9504   $213.95   $213.95   $214.00  
  Purchase #4 $126.86   4.465%   $132.5243   $132.52   $132.50   $132.50  
  Purchase #5 $56.74   7.724%   $61.1226   $61.12   $61.10   $61.10  
  Purchase #6 $163.66   4.665%   $171.2947   $171.29   $171.30   $171.30  
  Purchase #7 $36.40   7.742%   $39.2181   $39.22   $39.20   $39.20  
  7 purchase totals = $915.57       $969.0132   $969.00   $968.95   $969.00