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 $36.73   8.462%   $39.8381   $39.84   $39.85   $39.80  
  Purchase #2 $226.93   4.745%   $237.6978   $237.70   $237.70   $237.70  
  Purchase #3 $157.99   6.740%   $168.6385   $168.64   $168.65   $168.60  
  Purchase #4 $57.73   6.449%   $61.453   $61.45   $61.45   $61.50  
  Purchase #5 $221.62   8.788%   $241.096   $241.10   $241.10   $241.10  
  Purchase #6 $57.32   13.741%   $65.1963   $65.20   $65.20   $65.20  
  Purchase #7 $143.47   6.652%   $153.0136   $153.01   $153.00   $153.00  
  7 purchase totals = $901.79       $966.9333   $966.94   $966.95   $966.90