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 $30.61   10.257%   $33.7497   $33.75   $33.75   $33.70  
  Purchase #2 $105.96   4.356%   $110.5756   $110.58   $110.60   $110.60  
  Purchase #3 $31.77   6.313%   $33.7756   $33.78   $33.80   $33.80  
  Purchase #4 $248.67   4.666%   $260.2729   $260.27   $260.25   $260.30  
  Purchase #5 $131.35   6.640%   $140.0716   $140.07   $140.05   $140.10  
  Purchase #6 $189.81   10.592%   $209.9147   $209.91   $209.90   $209.90  
  Purchase #7 $164.86   13.181%   $186.5902   $186.59   $186.60   $186.60  
  7 purchase totals = $903.03       $974.9503   $974.95   $974.95   $975.00