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 $134.92   10.433%   $148.9962   $149.00   $149.00   $149.00  
  Purchase #2 $102.95   13.210%   $116.5497   $116.55   $116.55   $116.50  
  Purchase #3 $38.46   8.573%   $41.7572   $41.76   $41.75   $41.80  
  Purchase #4 $192.59   9.775%   $211.4157   $211.42   $211.40   $211.40  
  Purchase #5 $159.48   7.787%   $171.8987   $171.90   $171.90   $171.90  
  Purchase #6 $67.89   3.702%   $70.4033   $70.40   $70.40   $70.40  
  Purchase #7 $208.37   13.651%   $236.8146   $236.81   $236.80   $236.80  
  7 purchase totals = $904.66       $997.8354   $997.84   $997.80   $997.80