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 $143.55   7.517%   $154.3407   $154.34   $154.35   $154.30  
  Purchase #2 $91.96   4.425%   $96.0292   $96.03   $96.05   $96.00  
  Purchase #3 $143.80   7.822%   $155.048   $155.05   $155.05   $155.00  
  Purchase #4 $60.51   4.684%   $63.3443   $63.34   $63.35   $63.30  
  Purchase #5 $9.73   12.621%   $10.958   $10.96   $10.95   $11.00  
  Purchase #6 $228.35   3.499%   $236.34   $236.34   $236.35   $236.30  
  Purchase #7 $190.92   4.214%   $198.9654   $198.97   $198.95   $199.00  
  7 purchase totals = $868.82       $915.0256   $915.03   $915.05   $914.90