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 $96.62   6.401%   $102.8046   $102.80   $102.80   $102.80  
  Purchase #2 $97.58   7.797%   $105.1883   $105.19   $105.20   $105.20  
  Purchase #3 $86.72   11.872%   $97.0154   $97.02   $97.00   $97.00  
  Purchase #4 $167.59   9.149%   $182.9228   $182.92   $182.90   $182.90  
  Purchase #5 $205.28   3.380%   $212.2185   $212.22   $212.20   $212.20  
  Purchase #6 $161.48   13.300%   $182.9568   $182.96   $182.95   $183.00  
  Purchase #7 $130.25   13.396%   $147.6983   $147.70   $147.70   $147.70  
  7 purchase totals = $945.52       $1,030.8047   $1,030.81   $1,030.75   $1,030.80