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 $109.64   11.360%   $122.0951   $122.10   $122.10   $122.10  
  Purchase #2 $184.56   6.602%   $196.7447   $196.74   $196.75   $196.70  
  Purchase #3 $165.54   12.824%   $186.7688   $186.77   $186.75   $186.80  
  Purchase #4 $138.81   4.339%   $144.833   $144.83   $144.85   $144.80  
  Purchase #5 $88.66   7.825%   $95.5976   $95.60   $95.60   $95.60  
  Purchase #6 $243.75   10.451%   $269.2243   $269.22   $269.20   $269.20  
  Purchase #7 $224.39   9.553%   $245.826   $245.83   $245.85   $245.80  
  7 purchase totals = $1,155.35       $1,261.0895   $1,261.09   $1,261.10   $1,261.00