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 $226.83   11.870%   $253.7547   $253.75   $253.75   $253.80  
  Purchase #2 $157.74   3.473%   $163.2183   $163.22   $163.20   $163.20  
  Purchase #3 $205.55   10.600%   $227.3383   $227.34   $227.35   $227.30  
  Purchase #4 $127.50   12.679%   $143.6657   $143.67   $143.65   $143.70  
  Purchase #5 $231.42   6.806%   $247.1704   $247.17   $247.15   $247.20  
  Purchase #6 $25.36   6.639%   $27.0437   $27.04   $27.05   $27.00  
  Purchase #7 $118.65   4.104%   $123.5194   $123.52   $123.50   $123.50  
  7 purchase totals = $1,093.05       $1,185.7105   $1,185.71   $1,185.65   $1,185.70