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 $242.65   5.344%   $255.6172   $255.62   $255.60   $255.60  
  Purchase #2 $132.81   5.650%   $140.3138   $140.31   $140.30   $140.30  
  Purchase #3 $49.25   5.297%   $51.8588   $51.86   $51.85   $51.90  
  Purchase #4 $180.35   7.437%   $193.7626   $193.76   $193.75   $193.80  
  Purchase #5 $216.59   4.563%   $226.473   $226.47   $226.45   $226.50  
  Purchase #6 $34.67   5.421%   $36.5495   $36.55   $36.55   $36.50  
  Purchase #7 $108.87   8.585%   $118.2165   $118.22   $118.20   $118.20  
  7 purchase totals = $965.19       $1,022.7914   $1,022.79   $1,022.70   $1,022.80