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 $233.30   5.771%   $246.7637   $246.76   $246.75   $246.80  
  Purchase #2 $5.29   5.299%   $5.5703   $5.57   $5.55   $5.60  
  Purchase #3 $75.96   11.762%   $84.8944   $84.89   $84.90   $84.90  
  Purchase #4 $201.87   3.471%   $208.8769   $208.88   $208.90   $208.90  
  Purchase #5 $55.80   13.268%   $63.2035   $63.20   $63.20   $63.20  
  Purchase #6 $118.70   6.340%   $126.2256   $126.23   $126.25   $126.20  
  Purchase #7 $222.64   12.448%   $250.3542   $250.35   $250.35   $250.40  
  7 purchase totals = $913.56       $985.8886   $985.88   $985.90   $986.00