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 $146.49   7.591%   $157.6101   $157.61   $157.60   $157.60  
  Purchase #2 $231.95   6.456%   $246.9247   $246.92   $246.90   $246.90  
  Purchase #3 $235.92   8.632%   $256.2846   $256.28   $256.30   $256.30  
  Purchase #4 $103.65   4.784%   $108.6086   $108.61   $108.60   $108.60  
  Purchase #5 $62.38   5.407%   $65.7529   $65.75   $65.75   $65.80  
  Purchase #6 $175.92   6.229%   $186.8781   $186.88   $186.90   $186.90  
  Purchase #7 $32.99   5.806%   $34.9054   $34.91   $34.90   $34.90  
  7 purchase totals = $989.30       $1,056.9644   $1,056.96   $1,056.95   $1,057.00