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 $162.69   13.502%   $184.6564   $184.66   $184.65   $184.70  
  Purchase #2 $180.26   4.602%   $188.5556   $188.56   $188.55   $188.60  
  Purchase #3 $101.53   11.243%   $112.945   $112.95   $112.95   $112.90  
  Purchase #4 $139.43   8.376%   $151.1087   $151.11   $151.10   $151.10  
  Purchase #5 $220.65   3.527%   $228.4323   $228.43   $228.45   $228.40  
  Purchase #6 $121.89   11.165%   $135.499   $135.50   $135.50   $135.50  
  Purchase #7 $107.31   12.350%   $120.5628   $120.56   $120.55   $120.60  
  7 purchase totals = $1,033.76       $1,121.7598   $1,121.77   $1,121.75   $1,121.80