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 $62.47   6.458%   $66.5043   $66.50   $66.50   $66.50  
  Purchase #2 $206.82   10.764%   $229.0821   $229.08   $229.10   $229.10  
  Purchase #3 $63.42   9.550%   $69.4766   $69.48   $69.50   $69.50  
  Purchase #4 $31.45   8.487%   $34.1192   $34.12   $34.10   $34.10  
  Purchase #5 $10.30   6.658%   $10.9858   $10.99   $11.00   $11.00  
  Purchase #6 $43.92   6.129%   $46.6119   $46.61   $46.60   $46.60  
  Purchase #7 $176.93   5.729%   $187.0663   $187.07   $187.05   $187.10  
  7 purchase totals = $595.31       $643.8462   $643.85   $643.85   $643.90