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 $211.61   8.667%   $229.9502   $229.95   $229.95   $230.00  
  Purchase #2 $145.51   10.391%   $160.6299   $160.63   $160.65   $160.60  
  Purchase #3 $244.99   11.695%   $273.6416   $273.64   $273.65   $273.60  
  Purchase #4 $132.57   8.614%   $143.9896   $143.99   $144.00   $144.00  
  Purchase #5 $83.87   11.529%   $93.5394   $93.54   $93.55   $93.50  
  Purchase #6 $49.74   3.404%   $51.4331   $51.43   $51.45   $51.40  
  Purchase #7 $249.34   9.430%   $272.8528   $272.85   $272.85   $272.90  
  7 purchase totals = $1,117.63       $1,226.0366   $1,226.03   $1,226.10   $1,226.00