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 $91.47   5.257%   $96.2786   $96.28   $96.30   $96.30  
  Purchase #2 $70.87   8.592%   $76.9592   $76.96   $76.95   $77.00  
  Purchase #3 $227.29   10.300%   $250.7009   $250.70   $250.70   $250.70  
  Purchase #4 $48.46   13.634%   $55.067   $55.07   $55.05   $55.10  
  Purchase #5 $234.64   11.765%   $262.2454   $262.25   $262.25   $262.20  
  Purchase #6 $80.77   3.827%   $83.8611   $83.86   $83.85   $83.90  
  Purchase #7 $233.93   10.639%   $258.8178   $258.82   $258.80   $258.80  
  7 purchase totals = $987.43       $1,083.9300   $1,083.94   $1,083.90   $1,084.00