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 $210.59   11.807%   $235.4544   $235.45   $235.45   $235.50  
  Purchase #2 $213.98   8.202%   $231.5306   $231.53   $231.55   $231.50  
  Purchase #3 $9.47   13.558%   $10.7539   $10.75   $10.75   $10.80  
  Purchase #4 $210.77   7.764%   $227.1342   $227.13   $227.15   $227.10  
  Purchase #5 $73.76   8.540%   $80.0591   $80.06   $80.05   $80.10  
  Purchase #6 $101.42   12.569%   $114.1675   $114.17   $114.15   $114.20  
  Purchase #7 $148.47   12.160%   $166.524   $166.52   $166.50   $166.50  
  7 purchase totals = $968.46       $1,065.6237   $1,065.61   $1,065.60   $1,065.70