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 $89.52   5.857%   $94.7632   $94.76   $94.75   $94.80  
  Purchase #2 $112.32   4.740%   $117.644   $117.64   $117.65   $117.60  
  Purchase #3 $16.28   13.617%   $18.4968   $18.50   $18.50   $18.50  
  Purchase #4 $63.99   13.517%   $72.6395   $72.64   $72.65   $72.60  
  Purchase #5 $213.85   10.597%   $236.5117   $236.51   $236.50   $236.50  
  Purchase #6 $74.93   5.474%   $79.0317   $79.03   $79.05   $79.00  
  Purchase #7 $205.26   11.470%   $228.8033   $228.80   $228.80   $228.80  
  7 purchase totals = $776.15       $847.8902   $847.88   $847.90   $847.80