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 $157.64   10.115%   $173.5853   $173.59   $173.60   $173.60  
  Purchase #2 $217.63   10.174%   $239.7717   $239.77   $239.75   $239.80  
  Purchase #3 $97.72   13.570%   $110.9806   $110.98   $111.00   $111.00  
  Purchase #4 $64.54   12.284%   $72.4681   $72.47   $72.45   $72.50  
  Purchase #5 $194.78   9.598%   $213.475   $213.48   $213.50   $213.50  
  Purchase #6 $169.71   9.398%   $185.6593   $185.66   $185.65   $185.70  
  Purchase #7 $23.74   12.763%   $26.7699   $26.77   $26.75   $26.80  
  7 purchase totals = $925.76       $1,022.7099   $1,022.72   $1,022.70   $1,022.90