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 $220.69   11.790%   $246.7094   $246.71   $246.70   $246.70  
  Purchase #2 $237.73   13.131%   $268.9463   $268.95   $268.95   $268.90  
  Purchase #3 $33.57   7.639%   $36.1344   $36.13   $36.15   $36.10  
  Purchase #4 $216.63   10.410%   $239.1812   $239.18   $239.20   $239.20  
  Purchase #5 $149.47   12.135%   $167.6082   $167.61   $167.60   $167.60  
  Purchase #6 $180.28   6.755%   $192.4579   $192.46   $192.45   $192.50  
  Purchase #7 $180.78   12.264%   $202.9509   $202.95   $202.95   $203.00  
  7 purchase totals = $1,219.15       $1,353.9883   $1,353.99   $1,354.00   $1,354.00