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 $111.81   4.491%   $116.8314   $116.83   $116.85   $116.80  
  Purchase #2 $209.93   12.815%   $236.8325   $236.83   $236.85   $236.80  
  Purchase #3 $165.63   7.782%   $178.5193   $178.52   $178.50   $178.50  
  Purchase #4 $95.89   9.714%   $105.2048   $105.20   $105.20   $105.20  
  Purchase #5 $89.27   7.301%   $95.7876   $95.79   $95.80   $95.80  
  Purchase #6 $226.82   13.562%   $257.5813   $257.58   $257.60   $257.60  
  Purchase #7 $106.42   12.547%   $119.7725   $119.77   $119.75   $119.80  
  7 purchase totals = $1,005.77       $1,110.5294   $1,110.52   $1,110.55   $1,110.50