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 $57.71   10.620%   $63.8388   $63.84   $63.85   $63.80  
  Purchase #2 $227.80   5.339%   $239.9622   $239.96   $239.95   $240.00  
  Purchase #3 $25.32   9.283%   $27.6705   $27.67   $27.65   $27.70  
  Purchase #4 $186.42   6.255%   $198.0806   $198.08   $198.10   $198.10  
  Purchase #5 $101.78   13.339%   $115.3564   $115.36   $115.35   $115.40  
  Purchase #6 $177.47   9.248%   $193.8824   $193.88   $193.90   $193.90  
  Purchase #7 $151.43   9.518%   $165.8431   $165.84   $165.85   $165.80  
  7 purchase totals = $927.93       $1,004.6340   $1,004.63   $1,004.65   $1,004.70