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 $206.30   12.585%   $232.2629   $232.26   $232.25   $232.30  
  Purchase #2 $151.31   10.786%   $167.6303   $167.63   $167.65   $167.60  
  Purchase #3 $171.91   3.724%   $178.3119   $178.31   $178.30   $178.30  
  Purchase #4 $160.57   12.579%   $180.7681   $180.77   $180.75   $180.80  
  Purchase #5 $12.60   9.446%   $13.7902   $13.79   $13.80   $13.80  
  Purchase #6 $43.26   12.774%   $48.786   $48.79   $48.80   $48.80  
  Purchase #7 $217.39   5.661%   $229.6964   $229.70   $229.70   $229.70  
  7 purchase totals = $963.34       $1,051.2458   $1,051.25   $1,051.25   $1,051.30