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 $241.91   13.127%   $273.6655   $273.67   $273.65   $273.70  
  Purchase #2 $43.59   5.699%   $46.0742   $46.07   $46.05   $46.10  
  Purchase #3 $130.91   10.440%   $144.577   $144.58   $144.60   $144.60  
  Purchase #4 $182.45   6.699%   $194.6723   $194.67   $194.65   $194.70  
  Purchase #5 $14.66   7.314%   $15.7322   $15.73   $15.75   $15.70  
  Purchase #6 $241.93   5.124%   $254.3265   $254.33   $254.35   $254.30  
  Purchase #7 $95.48   11.353%   $106.3198   $106.32   $106.30   $106.30  
  7 purchase totals = $950.93       $1,035.3675   $1,035.37   $1,035.35   $1,035.40