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 $57.95   5.800%   $61.3111   $61.31   $61.30   $61.30  
  Purchase #2 $110.27   7.858%   $118.935   $118.94   $118.95   $118.90  
  Purchase #3 $108.66   4.154%   $113.1737   $113.17   $113.15   $113.20  
  Purchase #4 $41.44   12.656%   $46.6846   $46.68   $46.70   $46.70  
  Purchase #5 $136.84   5.276%   $144.0597   $144.06   $144.05   $144.10  
  Purchase #6 $201.36   3.255%   $207.9143   $207.91   $207.90   $207.90  
  Purchase #7 $87.42   10.264%   $96.3928   $96.39   $96.40   $96.40  
  7 purchase totals = $743.94       $788.4712   $788.46   $788.45   $788.50