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 $56.51   12.712%   $63.6936   $63.69   $63.70   $63.70  
  Purchase #2 $155.95   6.605%   $166.2505   $166.25   $166.25   $166.30  
  Purchase #3 $246.95   5.599%   $260.7767   $260.78   $260.80   $260.80  
  Purchase #4 $58.92   10.711%   $65.2309   $65.23   $65.25   $65.20  
  Purchase #5 $226.72   9.281%   $247.7619   $247.76   $247.75   $247.80  
  Purchase #6 $69.42   4.448%   $72.5078   $72.51   $72.50   $72.50  
  Purchase #7 $191.50   6.128%   $203.2351   $203.24   $203.25   $203.20  
  7 purchase totals = $1,005.97       $1,079.4565   $1,079.46   $1,079.50   $1,079.50