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 $240.61   5.153%   $253.0086   $253.01   $253.00   $253.00  
  Purchase #2 $134.61   4.707%   $140.9461   $140.95   $140.95   $140.90  
  Purchase #3 $88.52   7.458%   $95.1218   $95.12   $95.10   $95.10  
  Purchase #4 $61.46   13.827%   $69.9581   $69.96   $69.95   $70.00  
  Purchase #5 $114.38   3.759%   $118.6795   $118.68   $118.70   $118.70  
  Purchase #6 $20.86   5.499%   $22.0071   $22.01   $22.00   $22.00  
  Purchase #7 $74.27   9.522%   $81.342   $81.34   $81.35   $81.30  
  7 purchase totals = $734.71       $781.0632   $781.07   $781.05   $781.00