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 $49.26   13.639%   $55.9786   $55.98   $56.00   $56.00  
  Purchase #2 $146.42   12.394%   $164.5673   $164.57   $164.55   $164.60  
  Purchase #3 $71.72   11.416%   $79.9076   $79.91   $79.90   $79.90  
  Purchase #4 $171.70   7.507%   $184.5895   $184.59   $184.60   $184.60  
  Purchase #5 $24.36   8.714%   $26.4827   $26.48   $26.50   $26.50  
  Purchase #6 $127.32   11.798%   $142.3412   $142.34   $142.35   $142.30  
  Purchase #7 $92.56   9.238%   $101.1107   $101.11   $101.10   $101.10  
  7 purchase totals = $683.34       $754.9776   $754.98   $755.00   $755.00