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 $137.96   8.416%   $149.5707   $149.57   $149.55   $149.60  
  Purchase #2 $117.75   8.573%   $127.8447   $127.84   $127.85   $127.80  
  Purchase #3 $212.39   5.464%   $223.995   $224.00   $224.00   $224.00  
  Purchase #4 $105.37   9.262%   $115.1294   $115.13   $115.15   $115.10  
  Purchase #5 $67.28   11.241%   $74.8429   $74.84   $74.85   $74.80  
  Purchase #6 $239.63   4.352%   $250.0587   $250.06   $250.05   $250.10  
  Purchase #7 $118.58   6.364%   $126.1264   $126.13   $126.15   $126.10  
  7 purchase totals = $998.96       $1,067.5678   $1,067.57   $1,067.60   $1,067.50