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 $134.82   9.613%   $147.7802   $147.78   $147.80   $147.80  
  Purchase #2 $190.39   9.692%   $208.8426   $208.84   $208.85   $208.80  
  Purchase #3 $193.25   9.252%   $211.1295   $211.13   $211.15   $211.10  
  Purchase #4 $47.37   13.712%   $53.8654   $53.87   $53.85   $53.90  
  Purchase #5 $198.66   3.681%   $205.9727   $205.97   $205.95   $206.00  
  Purchase #6 $150.49   13.861%   $171.3494   $171.35   $171.35   $171.30  
  Purchase #7 $231.95   12.408%   $260.7304   $260.73   $260.75   $260.70  
  7 purchase totals = $1,146.93       $1,259.6702   $1,259.67   $1,259.70   $1,259.60