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 $149.25   8.568%   $162.0377   $162.04   $162.05   $162.00  
  Purchase #2 $16.46   11.365%   $18.3307   $18.33   $18.35   $18.30  
  Purchase #3 $170.91   6.808%   $182.5456   $182.55   $182.55   $182.50  
  Purchase #4 $100.29   7.313%   $107.6242   $107.62   $107.60   $107.60  
  Purchase #5 $80.28   12.389%   $90.2259   $90.23   $90.25   $90.20  
  Purchase #6 $246.40   8.364%   $267.0089   $267.01   $267.00   $267.00  
  Purchase #7 $51.87   13.180%   $58.7065   $58.71   $58.70   $58.70  
  7 purchase totals = $815.46       $886.4795   $886.49   $886.50   $886.30