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 $229.53   5.284%   $241.6584   $241.66   $241.65   $241.70  
  Purchase #2 $106.85   4.322%   $111.4681   $111.47   $111.45   $111.50  
  Purchase #3 $250.83   6.457%   $267.0261   $267.03   $267.05   $267.00  
  Purchase #4 $86.87   8.571%   $94.3156   $94.32   $94.30   $94.30  
  Purchase #5 $60.59   7.221%   $64.9652   $64.97   $64.95   $65.00  
  Purchase #6 $199.57   7.353%   $214.2444   $214.24   $214.25   $214.20  
  Purchase #7 $56.85   3.840%   $59.033   $59.03   $59.05   $59.00  
  7 purchase totals = $991.09       $1,052.7108   $1,052.72   $1,052.70   $1,052.70