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 $32.52   7.598%   $34.9909   $34.99   $35.00   $35.00  
  Purchase #2 $173.37   5.473%   $182.8585   $182.86   $182.85   $182.90  
  Purchase #3 $246.33   6.563%   $262.4966   $262.50   $262.50   $262.50  
  Purchase #4 $227.44   6.838%   $242.9923   $242.99   $243.00   $243.00  
  Purchase #5 $157.37   3.432%   $162.7709   $162.77   $162.75   $162.80  
  Purchase #6 $90.36   10.620%   $99.9562   $99.96   $99.95   $100.00  
  Purchase #7 $40.34   3.146%   $41.6091   $41.61   $41.60   $41.60  
  7 purchase totals = $967.73       $1,027.6745   $1,027.68   $1,027.65   $1,027.80