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 $112.48   12.870%   $126.9562   $126.96   $126.95   $127.00  
  Purchase #2 $68.99   5.869%   $73.039   $73.04   $73.05   $73.00  
  Purchase #3 $22.46   11.112%   $24.9558   $24.96   $24.95   $25.00  
  Purchase #4 $44.57   5.356%   $46.9572   $46.96   $46.95   $47.00  
  Purchase #5 $54.33   6.397%   $57.8055   $57.81   $57.80   $57.80  
  Purchase #6 $95.71   6.737%   $102.158   $102.16   $102.15   $102.20  
  Purchase #7 $236.51   4.138%   $246.2968   $246.30   $246.30   $246.30  
  7 purchase totals = $635.05       $678.1685   $678.19   $678.15   $678.30