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 $61.49   13.802%   $69.9768   $69.98   $70.00   $70.00  
  Purchase #2 $204.54   8.554%   $222.0364   $222.04   $222.05   $222.00  
  Purchase #3 $222.77   6.184%   $236.5461   $236.55   $236.55   $236.50  
  Purchase #4 $226.32   7.649%   $243.6312   $243.63   $243.65   $243.60  
  Purchase #5 $89.72   6.649%   $95.6855   $95.69   $95.70   $95.70  
  Purchase #6 $117.94   8.868%   $128.3989   $128.40   $128.40   $128.40  
  Purchase #7 $74.36   8.777%   $80.8866   $80.89   $80.90   $80.90  
  7 purchase totals = $997.14       $1,077.1615   $1,077.18   $1,077.25   $1,077.10