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 $55.36   7.405%   $59.4594   $59.46   $59.45   $59.50  
  Purchase #2 $125.67   6.818%   $134.2382   $134.24   $134.25   $134.20  
  Purchase #3 $82.61   5.533%   $87.1808   $87.18   $87.20   $87.20  
  Purchase #4 $129.60   3.709%   $134.4069   $134.41   $134.40   $134.40  
  Purchase #5 $113.36   3.426%   $117.2437   $117.24   $117.25   $117.20  
  Purchase #6 $229.98   8.711%   $250.0136   $250.01   $250.00   $250.00  
  Purchase #7 $220.77   7.426%   $237.1644   $237.16   $237.15   $237.20  
  7 purchase totals = $957.35       $1,019.7070   $1,019.70   $1,019.70   $1,019.70