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 $57.39   10.713%   $63.5382   $63.54   $63.55   $63.50  
  Purchase #2 $228.93   6.145%   $242.9977   $243.00   $243.00   $243.00  
  Purchase #3 $201.81   11.714%   $225.45   $225.45   $225.45   $225.50  
  Purchase #4 $225.41   11.213%   $250.6852   $250.69   $250.70   $250.70  
  Purchase #5 $134.73   5.753%   $142.481   $142.48   $142.50   $142.50  
  Purchase #6 $148.88   6.285%   $158.2371   $158.24   $158.25   $158.20  
  Purchase #7 $160.84   3.320%   $166.1799   $166.18   $166.20   $166.20  
  7 purchase totals = $1,157.99       $1,249.5691   $1,249.58   $1,249.65   $1,249.60