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 $147.83   8.298%   $160.0969   $160.10   $160.10   $160.10  
  Purchase #2 $36.31   9.173%   $39.6407   $39.64   $39.65   $39.60  
  Purchase #3 $207.83   9.748%   $228.0893   $228.09   $228.10   $228.10  
  Purchase #4 $214.58   6.151%   $227.7788   $227.78   $227.80   $227.80  
  Purchase #5 $147.57   4.282%   $153.8889   $153.89   $153.90   $153.90  
  Purchase #6 $83.46   8.593%   $90.6317   $90.63   $90.65   $90.60  
  Purchase #7 $107.55   6.643%   $114.6945   $114.69   $114.70   $114.70  
  7 purchase totals = $945.13       $1,014.8208   $1,014.82   $1,014.90   $1,014.80