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 $62.32   3.794%   $64.6844   $64.68   $64.70   $64.70  
  Purchase #2 $199.86   3.857%   $207.5686   $207.57   $207.55   $207.60  
  Purchase #3 $208.38   11.721%   $232.8042   $232.80   $232.80   $232.80  
  Purchase #4 $115.60   5.726%   $122.2193   $122.22   $122.20   $122.20  
  Purchase #5 $69.59   5.285%   $73.2678   $73.27   $73.25   $73.30  
  Purchase #6 $138.47   6.279%   $147.1645   $147.16   $147.15   $147.20  
  Purchase #7 $184.60   10.232%   $203.4883   $203.49   $203.50   $203.50  
  7 purchase totals = $978.82       $1,051.1971   $1,051.19   $1,051.15   $1,051.30