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 $106.59   8.137%   $115.2632   $115.26   $115.25   $115.30  
  Purchase #2 $67.36   12.780%   $75.9686   $75.97   $75.95   $76.00  
  Purchase #3 $147.94   6.665%   $157.8002   $157.80   $157.80   $157.80  
  Purchase #4 $137.43   12.319%   $154.36   $154.36   $154.35   $154.40  
  Purchase #5 $168.82   9.551%   $184.944   $184.94   $184.95   $184.90  
  Purchase #6 $75.97   9.419%   $83.1256   $83.13   $83.15   $83.10  
  Purchase #7 $243.99   7.169%   $261.4816   $261.48   $261.50   $261.50  
  7 purchase totals = $948.10       $1,032.9432   $1,032.94   $1,032.95   $1,033.00