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 $205.42   10.621%   $227.2377   $227.24   $227.25   $227.20  
  Purchase #2 $68.88   12.653%   $77.5954   $77.60   $77.60   $77.60  
  Purchase #3 $103.79   7.553%   $111.6293   $111.63   $111.65   $111.60  
  Purchase #4 $87.31   7.369%   $93.7439   $93.74   $93.75   $93.70  
  Purchase #5 $196.77   11.818%   $220.0243   $220.02   $220.00   $220.00  
  Purchase #6 $221.93   7.816%   $239.276   $239.28   $239.30   $239.30  
  Purchase #7 $245.91   3.348%   $254.1431   $254.14   $254.15   $254.10  
  7 purchase totals = $1,130.01       $1,223.6497   $1,223.65   $1,223.70   $1,223.50