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 $126.87   11.833%   $141.8825   $141.88   $141.90   $141.90  
  Purchase #2 $128.73   7.781%   $138.7465   $138.75   $138.75   $138.70  
  Purchase #3 $98.25   9.769%   $107.848   $107.85   $107.85   $107.80  
  Purchase #4 $212.44   4.824%   $222.6881   $222.69   $222.70   $222.70  
  Purchase #5 $64.72   5.235%   $68.1081   $68.11   $68.10   $68.10  
  Purchase #6 $145.60   8.244%   $157.6033   $157.60   $157.60   $157.60  
  Purchase #7 $131.36   13.434%   $149.0069   $149.01   $149.00   $149.00  
  7 purchase totals = $907.97       $985.8834   $985.89   $985.90   $985.80