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 $115.27   10.321%   $127.167   $127.17   $127.15   $127.20  
  Purchase #2 $193.52   4.621%   $202.4626   $202.46   $202.45   $202.50  
  Purchase #3 $59.35   4.866%   $62.238   $62.24   $62.25   $62.20  
  Purchase #4 $124.75   13.668%   $141.8008   $141.80   $141.80   $141.80  
  Purchase #5 $114.98   8.846%   $125.1511   $125.15   $125.15   $125.20  
  Purchase #6 $184.41   8.814%   $200.6639   $200.66   $200.65   $200.70  
  Purchase #7 $151.35   8.154%   $163.6911   $163.69   $163.70   $163.70  
  7 purchase totals = $943.63       $1,023.1745   $1,023.17   $1,023.15   $1,023.30