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 $225.71   11.634%   $251.9691   $251.97   $251.95   $252.00  
  Purchase #2 $50.69   5.139%   $53.295   $53.30   $53.30   $53.30  
  Purchase #3 $144.48   4.264%   $150.6406   $150.64   $150.65   $150.60  
  Purchase #4 $221.70   8.842%   $241.3027   $241.30   $241.30   $241.30  
  Purchase #5 $12.44   7.501%   $13.3731   $13.37   $13.35   $13.40  
  Purchase #6 $93.74   9.530%   $102.6734   $102.67   $102.65   $102.70  
  Purchase #7 $145.59   4.542%   $152.2027   $152.20   $152.20   $152.20  
  7 purchase totals = $894.35       $965.4566   $965.45   $965.40   $965.50