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 $108.97   9.126%   $118.9146   $118.91   $118.90   $118.90  
  Purchase #2 $212.87   9.712%   $233.5439   $233.54   $233.55   $233.50  
  Purchase #3 $64.80   12.216%   $72.716   $72.72   $72.70   $72.70  
  Purchase #4 $235.96   4.584%   $246.7764   $246.78   $246.80   $246.80  
  Purchase #5 $228.83   3.371%   $236.5439   $236.54   $236.55   $236.50  
  Purchase #6 $185.72   12.353%   $208.662   $208.66   $208.65   $208.70  
  Purchase #7 $230.75   13.768%   $262.5197   $262.52   $262.50   $262.50  
  7 purchase totals = $1,267.90       $1,379.6765   $1,379.67   $1,379.65   $1,379.60