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 $190.36   6.113%   $201.9967   $202.00   $202.00   $202.00  
  Purchase #2 $202.94   10.366%   $223.9768   $223.98   $224.00   $224.00  
  Purchase #3 $139.37   10.163%   $153.5342   $153.53   $153.55   $153.50  
  Purchase #4 $178.54   9.852%   $196.1298   $196.13   $196.15   $196.10  
  Purchase #5 $197.32   7.584%   $212.2847   $212.28   $212.30   $212.30  
  Purchase #6 $23.45   12.782%   $26.4474   $26.45   $26.45   $26.40  
  Purchase #7 $44.84   10.660%   $49.6199   $49.62   $49.60   $49.60  
  7 purchase totals = $976.82       $1,063.9895   $1,063.99   $1,064.05   $1,063.90