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 $136.93   11.466%   $152.6304   $152.63   $152.65   $152.60  
  Purchase #2 $206.64   11.548%   $230.5028   $230.50   $230.50   $230.50  
  Purchase #3 $220.70   7.831%   $237.983   $237.98   $238.00   $238.00  
  Purchase #4 $78.95   5.280%   $83.1186   $83.12   $83.10   $83.10  
  Purchase #5 $192.65   13.510%   $218.677   $218.68   $218.70   $218.70  
  Purchase #6 $246.41   7.339%   $264.494   $264.49   $264.50   $264.50  
  Purchase #7 $80.50   10.131%   $88.6555   $88.66   $88.65   $88.70  
  7 purchase totals = $1,162.78       $1,276.0613   $1,276.06   $1,276.10   $1,276.10