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 $63.49   5.492%   $66.9769   $66.98   $67.00   $67.00  
  Purchase #2 $116.48   3.690%   $120.7781   $120.78   $120.80   $120.80  
  Purchase #3 $173.49   7.160%   $185.9119   $185.91   $185.90   $185.90  
  Purchase #4 $48.97   6.583%   $52.1937   $52.19   $52.20   $52.20  
  Purchase #5 $120.62   11.644%   $134.665   $134.67   $134.65   $134.70  
  Purchase #6 $27.29   13.496%   $30.9731   $30.97   $30.95   $31.00  
  Purchase #7 $225.58   3.745%   $234.028   $234.03   $234.05   $234.00  
  7 purchase totals = $775.92       $825.5267   $825.53   $825.55   $825.60