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 $246.89   3.254%   $254.9238   $254.92   $254.90   $254.90  
  Purchase #2 $101.55   8.634%   $110.3178   $110.32   $110.30   $110.30  
  Purchase #3 $231.77   8.413%   $251.2688   $251.27   $251.25   $251.30  
  Purchase #4 $220.34   11.411%   $245.483   $245.48   $245.50   $245.50  
  Purchase #5 $46.36   3.543%   $48.0025   $48.00   $48.00   $48.00  
  Purchase #6 $129.81   9.720%   $142.4275   $142.43   $142.45   $142.40  
  Purchase #7 $50.83   10.696%   $56.2668   $56.27   $56.25   $56.30  
  7 purchase totals = $1,027.55       $1,108.6902   $1,108.69   $1,108.65   $1,108.70