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 $23.36   6.642%   $24.9116   $24.91   $24.90   $24.90  
  Purchase #2 $180.64   8.609%   $196.1913   $196.19   $196.20   $196.20  
  Purchase #3 $57.74   4.832%   $60.53   $60.53   $60.55   $60.50  
  Purchase #4 $183.46   6.188%   $194.8125   $194.81   $194.80   $194.80  
  Purchase #5 $88.57   12.522%   $99.6607   $99.66   $99.65   $99.70  
  Purchase #6 $108.52   9.831%   $119.1886   $119.19   $119.20   $119.20  
  Purchase #7 $169.46   13.828%   $192.8929   $192.89   $192.90   $192.90  
  7 purchase totals = $811.75       $888.1876   $888.18   $888.20   $888.20