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 $111.43   13.238%   $126.1811   $126.18   $126.20   $126.20  
  Purchase #2 $34.79   3.145%   $35.8841   $35.88   $35.90   $35.90  
  Purchase #3 $118.93   7.505%   $127.8557   $127.86   $127.85   $127.90  
  Purchase #4 $150.81   12.559%   $169.7502   $169.75   $169.75   $169.80  
  Purchase #5 $50.72   11.237%   $56.4194   $56.42   $56.40   $56.40  
  Purchase #6 $22.81   7.636%   $24.5518   $24.55   $24.55   $24.60  
  Purchase #7 $22.86   5.676%   $24.1575   $24.16   $24.15   $24.20  
  7 purchase totals = $512.35       $564.7998   $564.80   $564.80   $565.00