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 $243.78   6.634%   $259.9524   $259.95   $259.95   $260.00  
  Purchase #2 $71.66   9.416%   $78.4075   $78.41   $78.40   $78.40  
  Purchase #3 $6.26   12.234%   $7.0258   $7.03   $7.05   $7.00  
  Purchase #4 $58.79   12.610%   $66.2034   $66.20   $66.20   $66.20  
  Purchase #5 $85.53   11.488%   $95.3557   $95.36   $95.35   $95.40  
  Purchase #6 $153.43   6.616%   $163.5809   $163.58   $163.60   $163.60  
  Purchase #7 $70.77   5.417%   $74.6036   $74.60   $74.60   $74.60  
  7 purchase totals = $690.22       $745.1293   $745.13   $745.15   $745.20