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 $150.37   5.711%   $158.9576   $158.96   $158.95   $159.00  
  Purchase #2 $207.88   3.527%   $215.2119   $215.21   $215.20   $215.20  
  Purchase #3 $37.85   4.354%   $39.498   $39.50   $39.50   $39.50  
  Purchase #4 $47.85   5.127%   $50.3033   $50.30   $50.30   $50.30  
  Purchase #5 $234.60   12.614%   $264.1924   $264.19   $264.20   $264.20  
  Purchase #6 $208.29   10.867%   $230.9249   $230.92   $230.90   $230.90  
  Purchase #7 $92.25   3.816%   $95.7703   $95.77   $95.75   $95.80  
  7 purchase totals = $979.09       $1,054.8584   $1,054.85   $1,054.80   $1,054.90