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 $52.65   10.637%   $58.2504   $58.25   $58.25   $58.30  
  Purchase #2 $91.37   3.640%   $94.6959   $94.70   $94.70   $94.70  
  Purchase #3 $104.74   10.485%   $115.722   $115.72   $115.70   $115.70  
  Purchase #4 $161.56   9.328%   $176.6303   $176.63   $176.65   $176.60  
  Purchase #5 $220.97   4.549%   $231.0219   $231.02   $231.00   $231.00  
  Purchase #6 $83.36   11.303%   $92.7822   $92.78   $92.80   $92.80  
  Purchase #7 $238.26   9.787%   $261.5785   $261.58   $261.60   $261.60  
  7 purchase totals = $952.91       $1,030.6812   $1,030.68   $1,030.70   $1,030.70