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 $32.68   3.232%   $33.7362   $33.74   $33.75   $33.70  
  Purchase #2 $231.25   13.441%   $262.3323   $262.33   $262.35   $262.30  
  Purchase #3 $45.30   10.111%   $49.8803   $49.88   $49.90   $49.90  
  Purchase #4 $97.67   7.774%   $105.2629   $105.26   $105.25   $105.30  
  Purchase #5 $29.41   8.381%   $31.8749   $31.87   $31.85   $31.90  
  Purchase #6 $70.91   4.651%   $74.208   $74.21   $74.20   $74.20  
  Purchase #7 $65.99   5.556%   $69.6564   $69.66   $69.65   $69.70  
  7 purchase totals = $573.21       $626.9510   $626.95   $626.95   $627.00