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 $33.45   6.414%   $35.5955   $35.60   $35.60   $35.60  
  Purchase #2 $245.58   8.415%   $266.2456   $266.25   $266.25   $266.20  
  Purchase #3 $83.77   6.291%   $89.04   $89.04   $89.05   $89.00  
  Purchase #4 $179.40   8.566%   $194.7674   $194.77   $194.75   $194.80  
  Purchase #5 $134.49   9.110%   $146.742   $146.74   $146.75   $146.70  
  Purchase #6 $49.36   9.145%   $53.874   $53.87   $53.85   $53.90  
  Purchase #7 $200.34   8.863%   $218.0961   $218.10   $218.10   $218.10  
  7 purchase totals = $926.39       $1,004.3606   $1,004.37   $1,004.35   $1,004.30