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 $67.92   6.686%   $72.4611   $72.46   $72.45   $72.50  
  Purchase #2 $241.26   10.230%   $265.9409   $265.94   $265.95   $265.90  
  Purchase #3 $74.54   12.829%   $84.1027   $84.10   $84.10   $84.10  
  Purchase #4 $130.58   4.569%   $136.5462   $136.55   $136.55   $136.50  
  Purchase #5 $177.71   13.372%   $201.4734   $201.47   $201.45   $201.50  
  Purchase #6 $89.81   13.431%   $101.8724   $101.87   $101.85   $101.90  
  Purchase #7 $173.90   4.561%   $181.8316   $181.83   $181.85   $181.80  
  7 purchase totals = $955.72       $1,044.2283   $1,044.22   $1,044.20   $1,044.20