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 $44.76   11.154%   $49.7525   $49.75   $49.75   $49.80  
  Purchase #2 $184.98   9.397%   $202.3626   $202.36   $202.35   $202.40  
  Purchase #3 $191.40   4.658%   $200.3154   $200.32   $200.30   $200.30  
  Purchase #4 $239.83   5.331%   $252.6153   $252.62   $252.60   $252.60  
  Purchase #5 $100.43   10.766%   $111.2423   $111.24   $111.25   $111.20  
  Purchase #6 $129.35   12.667%   $145.7348   $145.73   $145.75   $145.70  
  Purchase #7 $16.82   9.795%   $18.4675   $18.47   $18.45   $18.50  
  7 purchase totals = $907.57       $980.4904   $980.49   $980.45   $980.50