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 $155.53   6.708%   $165.963   $165.96   $165.95   $166.00  
  Purchase #2 $247.65   13.339%   $280.684   $280.68   $280.70   $280.70  
  Purchase #3 $9.32   3.568%   $9.6525   $9.65   $9.65   $9.70  
  Purchase #4 $219.26   9.369%   $239.8025   $239.80   $239.80   $239.80  
  Purchase #5 $41.95   11.641%   $46.8334   $46.83   $46.85   $46.80  
  Purchase #6 $86.44   10.392%   $95.4228   $95.42   $95.40   $95.40  
  Purchase #7 $202.41   3.181%   $208.8487   $208.85   $208.85   $208.80  
  7 purchase totals = $962.56       $1,047.2069   $1,047.19   $1,047.20   $1,047.20