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 $54.68   11.832%   $61.1497   $61.15   $61.15   $61.10  
  Purchase #2 $30.28   7.839%   $32.6536   $32.65   $32.65   $32.70  
  Purchase #3 $23.89   6.395%   $25.4178   $25.42   $25.40   $25.40  
  Purchase #4 $169.79   3.612%   $175.9228   $175.92   $175.90   $175.90  
  Purchase #5 $222.58   6.230%   $236.4467   $236.45   $236.45   $236.40  
  Purchase #6 $236.71   12.239%   $265.6809   $265.68   $265.70   $265.70  
  Purchase #7 $224.67   6.176%   $238.5456   $238.55   $238.55   $238.50  
  7 purchase totals = $962.60       $1,035.8171   $1,035.82   $1,035.80   $1,035.70