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 $170.46   9.454%   $186.5753   $186.58   $186.60   $186.60  
  Purchase #2 $141.43   4.199%   $147.3686   $147.37   $147.35   $147.40  
  Purchase #3 $43.35   12.353%   $48.705   $48.71   $48.70   $48.70  
  Purchase #4 $211.25   9.573%   $231.473   $231.47   $231.45   $231.50  
  Purchase #5 $10.64   6.416%   $11.3227   $11.32   $11.30   $11.30  
  Purchase #6 $234.91   8.333%   $254.4851   $254.49   $254.50   $254.50  
  Purchase #7 $167.90   10.204%   $185.0325   $185.03   $185.05   $185.00  
  7 purchase totals = $979.94       $1,064.9622   $1,064.97   $1,064.95   $1,065.00