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 $238.74   10.406%   $263.5833   $263.58   $263.60   $263.60  
  Purchase #2 $90.34   12.590%   $101.7138   $101.71   $101.70   $101.70  
  Purchase #3 $68.67   6.652%   $73.2379   $73.24   $73.25   $73.20  
  Purchase #4 $204.52   5.609%   $215.9915   $215.99   $216.00   $216.00  
  Purchase #5 $193.68   6.208%   $205.7037   $205.70   $205.70   $205.70  
  Purchase #6 $61.37   10.680%   $67.9243   $67.92   $67.90   $67.90  
  Purchase #7 $95.87   11.465%   $106.8615   $106.86   $106.85   $106.90  
  7 purchase totals = $953.19       $1,035.0160   $1,035.00   $1,035.00   $1,035.00