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 $199.56   7.571%   $214.6687   $214.67   $214.65   $214.70  
  Purchase #2 $226.80   11.630%   $253.1768   $253.18   $253.20   $253.20  
  Purchase #3 $175.99   5.699%   $186.0197   $186.02   $186.00   $186.00  
  Purchase #4 $191.36   8.703%   $208.0141   $208.01   $208.00   $208.00  
  Purchase #5 $219.58   8.483%   $238.207   $238.21   $238.20   $238.20  
  Purchase #6 $70.72   5.618%   $74.693   $74.69   $74.70   $74.70  
  Purchase #7 $170.59   12.253%   $191.4924   $191.49   $191.50   $191.50  
  7 purchase totals = $1,254.60       $1,366.2717   $1,366.27   $1,366.25   $1,366.30