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 $223.48   11.123%   $248.3377   $248.34   $248.35   $248.30  
  Purchase #2 $234.66   13.174%   $265.5741   $265.57   $265.55   $265.60  
  Purchase #3 $204.70   8.210%   $221.5059   $221.51   $221.50   $221.50  
  Purchase #4 $83.93   10.427%   $92.6814   $92.68   $92.70   $92.70  
  Purchase #5 $16.67   4.843%   $17.4773   $17.48   $17.50   $17.50  
  Purchase #6 $71.50   11.768%   $79.9141   $79.91   $79.90   $79.90  
  Purchase #7 $126.61   8.644%   $137.5542   $137.55   $137.55   $137.60  
  7 purchase totals = $961.55       $1,063.0447   $1,063.04   $1,063.05   $1,063.10