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 $100.35   11.300%   $111.6896   $111.69   $111.70   $111.70  
  Purchase #2 $16.40   3.865%   $17.0339   $17.03   $17.05   $17.00  
  Purchase #3 $122.84   6.368%   $130.6625   $130.66   $130.65   $130.70  
  Purchase #4 $118.98   7.743%   $128.1926   $128.19   $128.20   $128.20  
  Purchase #5 $158.45   4.868%   $166.1633   $166.16   $166.15   $166.20  
  Purchase #6 $220.60   10.732%   $244.2748   $244.27   $244.25   $244.30  
  Purchase #7 $115.87   4.395%   $120.9625   $120.96   $120.95   $121.00  
  7 purchase totals = $853.49       $918.9792   $918.96   $918.95   $919.10