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 $158.31   9.626%   $173.5489   $173.55   $173.55   $173.50  
  Purchase #2 $35.32   8.348%   $38.2685   $38.27   $38.25   $38.30  
  Purchase #3 $60.86   9.464%   $66.6198   $66.62   $66.60   $66.60  
  Purchase #4 $211.74   10.320%   $233.5916   $233.59   $233.60   $233.60  
  Purchase #5 $153.35   12.532%   $172.5678   $172.57   $172.55   $172.60  
  Purchase #6 $142.58   10.134%   $157.0291   $157.03   $157.05   $157.00  
  Purchase #7 $44.30   12.131%   $49.674   $49.67   $49.65   $49.70  
  7 purchase totals = $806.46       $891.2997   $891.30   $891.25   $891.30