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 $240.36   6.510%   $256.0074   $256.01   $256.00   $256.00  
  Purchase #2 $247.67   12.593%   $278.8591   $278.86   $278.85   $278.90  
  Purchase #3 $196.39   3.326%   $202.9219   $202.92   $202.90   $202.90  
  Purchase #4 $21.68   7.769%   $23.3643   $23.36   $23.35   $23.40  
  Purchase #5 $25.28   4.543%   $26.4285   $26.43   $26.45   $26.40  
  Purchase #6 $183.67   10.485%   $202.9278   $202.93   $202.95   $202.90  
  Purchase #7 $196.53   7.772%   $211.8043   $211.80   $211.80   $211.80  
  7 purchase totals = $1,111.58       $1,202.3133   $1,202.31   $1,202.30   $1,202.30