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 $124.46   9.746%   $136.5899   $136.59   $136.60   $136.60  
  Purchase #2 $200.72   7.821%   $216.4183   $216.42   $216.40   $216.40  
  Purchase #3 $196.91   10.411%   $217.4103   $217.41   $217.40   $217.40  
  Purchase #4 $56.47   6.836%   $60.3303   $60.33   $60.35   $60.30  
  Purchase #5 $72.92   9.285%   $79.6906   $79.69   $79.70   $79.70  
  Purchase #6 $153.97   9.377%   $168.4078   $168.41   $168.40   $168.40  
  Purchase #7 $203.51   6.456%   $216.6486   $216.65   $216.65   $216.60  
  7 purchase totals = $1,008.96       $1,095.4958   $1,095.50   $1,095.50   $1,095.40