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 $29.97   7.782%   $32.3023   $32.30   $32.30   $32.30  
  Purchase #2 $245.76   9.436%   $268.9499   $268.95   $268.95   $268.90  
  Purchase #3 $242.45   6.590%   $258.4275   $258.43   $258.45   $258.40  
  Purchase #4 $231.77   4.735%   $242.7443   $242.74   $242.75   $242.70  
  Purchase #5 $234.40   13.120%   $265.1533   $265.15   $265.15   $265.20  
  Purchase #6 $122.33   12.416%   $137.5185   $137.52   $137.50   $137.50  
  Purchase #7 $169.93   6.509%   $180.9907   $180.99   $181.00   $181.00  
  7 purchase totals = $1,276.61       $1,386.0865   $1,386.08   $1,386.10   $1,386.00