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 $207.58   7.303%   $222.7396   $222.74   $222.75   $222.70  
  Purchase #2 $10.29   9.705%   $11.2886   $11.29   $11.30   $11.30  
  Purchase #3 $67.33   13.398%   $76.3509   $76.35   $76.35   $76.40  
  Purchase #4 $18.43   5.429%   $19.4306   $19.43   $19.45   $19.40  
  Purchase #5 $242.95   9.514%   $266.0643   $266.06   $266.05   $266.10  
  Purchase #6 $161.66   4.737%   $169.3178   $169.32   $169.30   $169.30  
  Purchase #7 $20.41   11.753%   $22.8088   $22.81   $22.80   $22.80  
  7 purchase totals = $728.65       $788.0006   $788.00   $788.00   $788.00