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   4.394%   $252.5395   $252.54   $252.55   $252.50  
  Purchase #2 $176.56   11.413%   $196.7108   $196.71   $196.70   $196.70  
  Purchase #3 $232.74   13.356%   $263.8248   $263.82   $263.80   $263.80  
  Purchase #4 $187.95   4.199%   $195.842   $195.84   $195.85   $195.80  
  Purchase #5 $188.55   10.733%   $208.7871   $208.79   $208.80   $208.80  
  Purchase #6 $172.93   8.751%   $188.0631   $188.06   $188.05   $188.10  
  Purchase #7 $33.74   6.308%   $35.8683   $35.87   $35.85   $35.90  
  7 purchase totals = $1,234.38       $1,341.6356   $1,341.63   $1,341.60   $1,341.60