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 $158.83   5.175%   $167.0495   $167.05   $167.05   $167.00  
  Purchase #2 $87.30   6.113%   $92.6366   $92.64   $92.65   $92.60  
  Purchase #3 $110.70   12.496%   $124.5331   $124.53   $124.55   $124.50  
  Purchase #4 $207.28   6.577%   $220.9128   $220.91   $220.90   $220.90  
  Purchase #5 $237.87   11.834%   $266.0195   $266.02   $266.00   $266.00  
  Purchase #6 $50.67   4.362%   $52.8802   $52.88   $52.90   $52.90  
  Purchase #7 $17.87   6.346%   $19.004   $19.00   $19.00   $19.00  
  7 purchase totals = $870.52       $943.0357   $943.03   $943.05   $942.90