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 $60.94   12.552%   $68.5892   $68.59   $68.60   $68.60  
  Purchase #2 $198.97   9.824%   $218.5168   $218.52   $218.50   $218.50  
  Purchase #3 $117.92   3.773%   $122.3691   $122.37   $122.35   $122.40  
  Purchase #4 $180.33   5.132%   $189.5845   $189.58   $189.60   $189.60  
  Purchase #5 $122.68   6.770%   $130.9854   $130.99   $131.00   $131.00  
  Purchase #6 $54.31   12.111%   $60.8875   $60.89   $60.90   $60.90  
  Purchase #7 $107.57   3.580%   $111.421   $111.42   $111.40   $111.40  
  7 purchase totals = $842.72       $902.3535   $902.36   $902.35   $902.40