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 $84.34   5.783%   $89.2174   $89.22   $89.20   $89.20  
  Purchase #2 $247.40   5.639%   $261.3509   $261.35   $261.35   $261.40  
  Purchase #3 $25.50   3.165%   $26.3071   $26.31   $26.30   $26.30  
  Purchase #4 $91.37   6.105%   $96.9481   $96.95   $96.95   $96.90  
  Purchase #5 $98.64   12.113%   $110.5883   $110.59   $110.60   $110.60  
  Purchase #6 $250.77   10.516%   $277.141   $277.14   $277.15   $277.10  
  Purchase #7 $173.84   4.540%   $181.7323   $181.73   $181.75   $181.70  
  7 purchase totals = $971.86       $1,043.2851   $1,043.29   $1,043.30   $1,043.20