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 $214.25   13.763%   $243.7372   $243.74   $243.75   $243.70  
  Purchase #2 $68.45   6.174%   $72.6761   $72.68   $72.70   $72.70  
  Purchase #3 $61.51   7.116%   $65.8871   $65.89   $65.90   $65.90  
  Purchase #4 $131.55   5.662%   $138.9984   $139.00   $139.00   $139.00  
  Purchase #5 $91.77   11.140%   $101.9932   $101.99   $102.00   $102.00  
  Purchase #6 $22.35   11.769%   $24.9804   $24.98   $25.00   $25.00  
  Purchase #7 $135.34   6.645%   $144.3333   $144.33   $144.35   $144.30  
  7 purchase totals = $725.22       $792.6057   $792.61   $792.70   $792.60