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 $32.45   5.794%   $34.3302   $34.33   $34.35   $34.30  
  Purchase #2 $55.45   8.209%   $60.0019   $60.00   $60.00   $60.00  
  Purchase #3 $96.73   4.329%   $100.9174   $100.92   $100.90   $100.90  
  Purchase #4 $232.30   9.219%   $253.7157   $253.72   $253.70   $253.70  
  Purchase #5 $33.88   13.575%   $38.4792   $38.48   $38.50   $38.50  
  Purchase #6 $88.77   8.838%   $96.6155   $96.62   $96.60   $96.60  
  Purchase #7 $167.46   7.526%   $180.063   $180.06   $180.05   $180.10  
  7 purchase totals = $707.04       $764.1229   $764.13   $764.10   $764.10