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 $206.87   9.402%   $226.3199   $226.32   $226.30   $226.30  
  Purchase #2 $45.65   6.479%   $48.6077   $48.61   $48.60   $48.60  
  Purchase #3 $74.89   7.252%   $80.321   $80.32   $80.30   $80.30  
  Purchase #4 $216.94   7.459%   $233.1216   $233.12   $233.10   $233.10  
  Purchase #5 $239.69   6.671%   $255.6797   $255.68   $255.70   $255.70  
  Purchase #6 $8.78   6.692%   $9.3676   $9.37   $9.35   $9.40  
  Purchase #7 $195.51   6.384%   $207.9914   $207.99   $208.00   $208.00  
  7 purchase totals = $988.33       $1,061.4089   $1,061.41   $1,061.35   $1,061.40