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 $41.86   6.531%   $44.5939   $44.59   $44.60   $44.60  
  Purchase #2 $129.34   4.376%   $134.9999   $135.00   $135.00   $135.00  
  Purchase #3 $176.82   12.518%   $198.9543   $198.95   $198.95   $199.00  
  Purchase #4 $71.26   12.358%   $80.0663   $80.07   $80.05   $80.10  
  Purchase #5 $246.67   3.368%   $254.9778   $254.98   $255.00   $255.00  
  Purchase #6 $237.30   12.766%   $267.5937   $267.59   $267.60   $267.60  
  Purchase #7 $100.58   5.786%   $106.3996   $106.40   $106.40   $106.40  
  7 purchase totals = $1,003.83       $1,087.5855   $1,087.58   $1,087.60   $1,087.70