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 $60.71   8.692%   $65.9869   $65.99   $66.00   $66.00  
  Purchase #2 $70.28   6.198%   $74.636   $74.64   $74.65   $74.60  
  Purchase #3 $244.69   4.436%   $255.5444   $255.54   $255.55   $255.50  
  Purchase #4 $206.83   9.701%   $226.8946   $226.89   $226.90   $226.90  
  Purchase #5 $121.54   11.779%   $135.8562   $135.86   $135.85   $135.90  
  Purchase #6 $180.91   7.297%   $194.111   $194.11   $194.10   $194.10  
  Purchase #7 $224.47   12.617%   $252.7914   $252.79   $252.80   $252.80  
  7 purchase totals = $1,109.43       $1,205.8205   $1,205.82   $1,205.85   $1,205.80