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 $62.86   5.451%   $66.2865   $66.29   $66.30   $66.30  
  Purchase #2 $173.89   4.246%   $181.2734   $181.27   $181.25   $181.30  
  Purchase #3 $52.27   7.713%   $56.3016   $56.30   $56.30   $56.30  
  Purchase #4 $28.41   4.397%   $29.6592   $29.66   $29.65   $29.70  
  Purchase #5 $74.36   5.341%   $78.3316   $78.33   $78.35   $78.30  
  Purchase #6 $89.62   7.283%   $96.147   $96.15   $96.15   $96.10  
  Purchase #7 $12.43   12.575%   $13.9931   $13.99   $14.00   $14.00  
  7 purchase totals = $493.84       $521.9924   $521.99   $522.00   $522.00