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 $31.48   11.117%   $34.9796   $34.98   $35.00   $35.00  
  Purchase #2 $149.27   8.357%   $161.7445   $161.74   $161.75   $161.70  
  Purchase #3 $245.39   9.728%   $269.2615   $269.26   $269.25   $269.30  
  Purchase #4 $56.68   6.310%   $60.2565   $60.26   $60.25   $60.30  
  Purchase #5 $136.86   9.506%   $149.8699   $149.87   $149.85   $149.90  
  Purchase #6 $185.76   12.303%   $208.6141   $208.61   $208.60   $208.60  
  Purchase #7 $91.52   8.823%   $99.5948   $99.59   $99.60   $99.60  
  7 purchase totals = $896.96       $984.3209   $984.31   $984.30   $984.40