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 $96.98   6.615%   $103.3952   $103.40   $103.40   $103.40  
  Purchase #2 $242.83   13.625%   $275.9156   $275.92   $275.90   $275.90  
  Purchase #3 $7.74   12.549%   $8.7113   $8.71   $8.70   $8.70  
  Purchase #4 $195.36   13.613%   $221.9544   $221.95   $221.95   $222.00  
  Purchase #5 $134.46   8.108%   $145.362   $145.36   $145.35   $145.40  
  Purchase #6 $182.40   12.787%   $205.7235   $205.72   $205.70   $205.70  
  Purchase #7 $43.38   9.286%   $47.4083   $47.41   $47.40   $47.40  
  7 purchase totals = $903.15       $1,008.4703   $1,008.47   $1,008.40   $1,008.50