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 $57.95   4.784%   $60.7223   $60.72   $60.70   $60.70  
  Purchase #2 $9.48   9.837%   $10.4125   $10.41   $10.40   $10.40  
  Purchase #3 $88.84   11.119%   $98.7181   $98.72   $98.70   $98.70  
  Purchase #4 $234.61   13.820%   $267.0331   $267.03   $267.05   $267.00  
  Purchase #5 $43.49   5.652%   $45.9481   $45.95   $45.95   $45.90  
  Purchase #6 $219.46   3.870%   $227.9531   $227.95   $227.95   $228.00  
  Purchase #7 $33.80   7.287%   $36.263   $36.26   $36.25   $36.30  
  7 purchase totals = $687.63       $747.0502   $747.04   $747.00   $747.00