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 $239.33   10.726%   $265.0005   $265.00   $265.00   $265.00  
  Purchase #2 $165.93   7.327%   $178.0877   $178.09   $178.10   $178.10  
  Purchase #3 $13.54   6.349%   $14.3997   $14.40   $14.40   $14.40  
  Purchase #4 $147.56   6.437%   $157.0584   $157.06   $157.05   $157.10  
  Purchase #5 $239.63   11.817%   $267.9471   $267.95   $267.95   $267.90  
  Purchase #6 $234.87   4.731%   $245.9817   $245.98   $246.00   $246.00  
  Purchase #7 $218.91   6.814%   $233.8265   $233.83   $233.85   $233.80  
  7 purchase totals = $1,259.77       $1,362.3016   $1,362.31   $1,362.35   $1,362.30