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 $97.40   8.230%   $105.416   $105.42   $105.40   $105.40  
  Purchase #2 $198.95   10.595%   $220.0288   $220.03   $220.05   $220.00  
  Purchase #3 $50.97   6.679%   $54.3743   $54.37   $54.35   $54.40  
  Purchase #4 $87.92   3.693%   $91.1669   $91.17   $91.15   $91.20  
  Purchase #5 $84.45   6.719%   $90.1242   $90.12   $90.10   $90.10  
  Purchase #6 $247.83   3.715%   $257.0369   $257.04   $257.05   $257.00  
  Purchase #7 $243.91   12.845%   $275.2402   $275.24   $275.25   $275.20  
  7 purchase totals = $1,011.43       $1,093.3873   $1,093.39   $1,093.35   $1,093.30