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 $30.66   6.315%   $32.5962   $32.60   $32.60   $32.60  
  Purchase #2 $237.69   11.510%   $265.0481   $265.05   $265.05   $265.00  
  Purchase #3 $93.65   12.619%   $105.4677   $105.47   $105.45   $105.50  
  Purchase #4 $243.55   5.563%   $257.0987   $257.10   $257.10   $257.10  
  Purchase #5 $167.86   9.136%   $183.1957   $183.20   $183.20   $183.20  
  Purchase #6 $16.67   4.217%   $17.373   $17.37   $17.35   $17.40  
  Purchase #7 $192.44   10.406%   $212.4653   $212.47   $212.45   $212.50  
  7 purchase totals = $982.52       $1,073.2447   $1,073.26   $1,073.20   $1,073.30