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 $77.47   10.529%   $85.6268   $85.63   $85.65   $85.60  
  Purchase #2 $248.82   5.687%   $262.9704   $262.97   $262.95   $263.00  
  Purchase #3 $228.87   10.805%   $253.5994   $253.60   $253.60   $253.60  
  Purchase #4 $181.65   9.251%   $198.4544   $198.45   $198.45   $198.50  
  Purchase #5 $72.64   5.587%   $76.6984   $76.70   $76.70   $76.70  
  Purchase #6 $48.34   9.634%   $52.9971   $53.00   $53.00   $53.00  
  Purchase #7 $31.89   6.555%   $33.9804   $33.98   $34.00   $34.00  
  7 purchase totals = $889.68       $964.3269   $964.33   $964.35   $964.40