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 $218.59   6.611%   $233.041   $233.04   $233.05   $233.00  
  Purchase #2 $151.96   7.677%   $163.626   $163.63   $163.65   $163.60  
  Purchase #3 $83.41   4.654%   $87.2919   $87.29   $87.30   $87.30  
  Purchase #4 $236.62   8.796%   $257.4331   $257.43   $257.45   $257.40  
  Purchase #5 $184.92   13.523%   $209.9267   $209.93   $209.95   $209.90  
  Purchase #6 $125.50   12.410%   $141.0746   $141.07   $141.05   $141.10  
  Purchase #7 $207.52   4.466%   $216.7878   $216.79   $216.80   $216.80  
  7 purchase totals = $1,208.52       $1,309.1811   $1,309.18   $1,309.25   $1,309.10