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 $170.61   13.489%   $193.6236   $193.62   $193.60   $193.60  
  Purchase #2 $5.87   9.446%   $6.4245   $6.42   $6.40   $6.40  
  Purchase #3 $176.69   8.255%   $191.2758   $191.28   $191.30   $191.30  
  Purchase #4 $195.55   5.256%   $205.8281   $205.83   $205.85   $205.80  
  Purchase #5 $167.85   4.834%   $175.9639   $175.96   $175.95   $176.00  
  Purchase #6 $82.50   9.799%   $90.5842   $90.58   $90.60   $90.60  
  Purchase #7 $80.88   12.509%   $90.9973   $91.00   $91.00   $91.00  
  7 purchase totals = $879.95       $954.6974   $954.69   $954.70   $954.70