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 $86.41   8.797%   $94.0115   $94.01   $94.00   $94.00  
  Purchase #2 $126.97   10.269%   $140.0085   $140.01   $140.00   $140.00  
  Purchase #3 $230.31   4.121%   $239.8011   $239.80   $239.80   $239.80  
  Purchase #4 $146.31   12.718%   $164.9177   $164.92   $164.90   $164.90  
  Purchase #5 $207.68   7.147%   $222.5229   $222.52   $222.50   $222.50  
  Purchase #6 $161.35   7.476%   $173.4125   $173.41   $173.40   $173.40  
  Purchase #7 $62.61   10.178%   $68.9824   $68.98   $69.00   $69.00  
  7 purchase totals = $1,021.64       $1,103.6566   $1,103.65   $1,103.60   $1,103.60