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 $60.50   6.323%   $64.3254   $64.33   $64.35   $64.30  
  Purchase #2 $114.45   8.426%   $124.0936   $124.09   $124.10   $124.10  
  Purchase #3 $113.50   3.675%   $117.6711   $117.67   $117.65   $117.70  
  Purchase #4 $61.44   7.370%   $65.9681   $65.97   $65.95   $66.00  
  Purchase #5 $211.48   4.599%   $221.206   $221.21   $221.20   $221.20  
  Purchase #6 $143.34   12.296%   $160.9651   $160.97   $160.95   $161.00  
  Purchase #7 $10.64   5.144%   $11.1873   $11.19   $11.20   $11.20  
  7 purchase totals = $715.35       $765.4166   $765.43   $765.40   $765.50