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 $56.53   7.473%   $60.7545   $60.75   $60.75   $60.80  
  Purchase #2 $232.85   4.167%   $242.5529   $242.55   $242.55   $242.60  
  Purchase #3 $115.91   3.304%   $119.7397   $119.74   $119.75   $119.70  
  Purchase #4 $192.35   12.847%   $217.0612   $217.06   $217.05   $217.10  
  Purchase #5 $191.40   6.595%   $204.0228   $204.02   $204.00   $204.00  
  Purchase #6 $177.38   5.236%   $186.6676   $186.67   $186.65   $186.70  
  Purchase #7 $8.48   12.107%   $9.5067   $9.51   $9.50   $9.50  
  7 purchase totals = $974.90       $1,040.3054   $1,040.30   $1,040.25   $1,040.40