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 $204.37   5.834%   $216.2929   $216.29   $216.30   $216.30  
  Purchase #2 $91.58   3.707%   $94.9749   $94.97   $94.95   $95.00  
  Purchase #3 $26.89   3.198%   $27.7499   $27.75   $27.75   $27.70  
  Purchase #4 $232.60   8.366%   $252.0593   $252.06   $252.05   $252.10  
  Purchase #5 $113.70   7.421%   $122.1377   $122.14   $122.15   $122.10  
  Purchase #6 $194.97   6.157%   $206.9743   $206.97   $206.95   $207.00  
  Purchase #7 $127.71   8.708%   $138.831   $138.83   $138.85   $138.80  
  7 purchase totals = $991.82       $1,059.0200   $1,059.01   $1,059.00   $1,059.00