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 $34.41   6.503%   $36.6477   $36.65   $36.65   $36.60  
  Purchase #2 $249.55   13.598%   $283.4838   $283.48   $283.50   $283.50  
  Purchase #3 $101.90   13.182%   $115.3325   $115.33   $115.35   $115.30  
  Purchase #4 $246.81   5.701%   $260.8806   $260.88   $260.90   $260.90  
  Purchase #5 $221.35   9.717%   $242.8586   $242.86   $242.85   $242.90  
  Purchase #6 $155.40   8.685%   $168.8965   $168.90   $168.90   $168.90  
  Purchase #7 $130.93   4.377%   $136.6608   $136.66   $136.65   $136.70  
  7 purchase totals = $1,140.35       $1,244.7605   $1,244.76   $1,244.80   $1,244.80