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 $211.47   8.199%   $228.8084   $228.81   $228.80   $228.80  
  Purchase #2 $228.95   3.207%   $236.2924   $236.29   $236.30   $236.30  
  Purchase #3 $160.32   7.709%   $172.6791   $172.68   $172.70   $172.70  
  Purchase #4 $231.85   11.215%   $257.852   $257.85   $257.85   $257.90  
  Purchase #5 $207.63   7.300%   $222.787   $222.79   $222.80   $222.80  
  Purchase #6 $46.77   7.747%   $50.3933   $50.39   $50.40   $50.40  
  Purchase #7 $15.51   6.732%   $16.5541   $16.55   $16.55   $16.60  
  7 purchase totals = $1,102.50       $1,185.3663   $1,185.36   $1,185.40   $1,185.50