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 $224.58   3.748%   $232.9973   $233.00   $233.00   $233.00  
  Purchase #2 $68.85   3.197%   $71.0511   $71.05   $71.05   $71.10  
  Purchase #3 $23.89   5.325%   $25.1621   $25.16   $25.15   $25.20  
  Purchase #4 $82.46   11.371%   $91.8365   $91.84   $91.85   $91.80  
  Purchase #5 $181.64   3.768%   $188.4842   $188.48   $188.50   $188.50  
  Purchase #6 $152.82   11.871%   $170.9613   $170.96   $170.95   $171.00  
  Purchase #7 $230.83   7.434%   $247.9899   $247.99   $248.00   $248.00  
  7 purchase totals = $965.07       $1,028.4824   $1,028.48   $1,028.50   $1,028.60