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 $248.30   13.141%   $280.9291   $280.93   $280.95   $280.90  
  Purchase #2 $202.85   6.822%   $216.6884   $216.69   $216.70   $216.70  
  Purchase #3 $44.58   4.400%   $46.5415   $46.54   $46.55   $46.50  
  Purchase #4 $124.68   5.612%   $131.677   $131.68   $131.70   $131.70  
  Purchase #5 $228.49   5.414%   $240.8604   $240.86   $240.85   $240.90  
  Purchase #6 $125.73   9.124%   $137.2016   $137.20   $137.20   $137.20  
  Purchase #7 $135.84   8.582%   $147.4978   $147.50   $147.50   $147.50  
  7 purchase totals = $1,110.47       $1,201.3958   $1,201.40   $1,201.45   $1,201.40