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 $209.92   11.469%   $233.9957   $234.00   $234.00   $234.00  
  Purchase #2 $119.33   8.372%   $129.3203   $129.32   $129.30   $129.30  
  Purchase #3 $68.39   12.619%   $77.0201   $77.02   $77.00   $77.00  
  Purchase #4 $243.65   10.758%   $269.8619   $269.86   $269.85   $269.90  
  Purchase #5 $226.26   7.564%   $243.3743   $243.37   $243.35   $243.40  
  Purchase #6 $203.38   9.173%   $222.036   $222.04   $222.05   $222.00  
  Purchase #7 $245.81   5.670%   $259.7474   $259.75   $259.75   $259.70  
  7 purchase totals = $1,316.74       $1,435.3557   $1,435.36   $1,435.30   $1,435.30