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 $58.36   9.136%   $63.6918   $63.69   $63.70   $63.70  
  Purchase #2 $122.95   4.276%   $128.2073   $128.21   $128.20   $128.20  
  Purchase #3 $226.26   6.138%   $240.1478   $240.15   $240.15   $240.10  
  Purchase #4 $207.96   9.122%   $226.9301   $226.93   $226.95   $226.90  
  Purchase #5 $206.99   10.245%   $228.1961   $228.20   $228.20   $228.20  
  Purchase #6 $202.45   3.148%   $208.8231   $208.82   $208.80   $208.80  
  Purchase #7 $156.43   3.409%   $161.7627   $161.76   $161.75   $161.80  
  7 purchase totals = $1,181.40       $1,257.7589   $1,257.76   $1,257.75   $1,257.70