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 $98.60   6.270%   $104.7822   $104.78   $104.80   $104.80  
  Purchase #2 $132.57   9.509%   $145.1761   $145.18   $145.20   $145.20  
  Purchase #3 $238.46   6.587%   $254.1674   $254.17   $254.15   $254.20  
  Purchase #4 $235.64   4.211%   $245.5628   $245.56   $245.55   $245.60  
  Purchase #5 $203.66   8.776%   $221.5332   $221.53   $221.55   $221.50  
  Purchase #6 $28.95   3.239%   $29.8877   $29.89   $29.90   $29.90  
  Purchase #7 $60.93   9.676%   $66.8256   $66.83   $66.85   $66.80  
  7 purchase totals = $998.81       $1,067.9350   $1,067.94   $1,068.00   $1,068.00