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 $190.93   8.414%   $206.9949   $206.99   $207.00   $207.00  
  Purchase #2 $228.44   10.179%   $251.6929   $251.69   $251.70   $251.70  
  Purchase #3 $53.81   5.147%   $56.5796   $56.58   $56.60   $56.60  
  Purchase #4 $196.94   4.463%   $205.7294   $205.73   $205.75   $205.70  
  Purchase #5 $233.82   11.130%   $259.8442   $259.84   $259.85   $259.80  
  Purchase #6 $11.45   7.864%   $12.3504   $12.35   $12.35   $12.40  
  Purchase #7 $220.96   9.502%   $241.9556   $241.96   $241.95   $242.00  
  7 purchase totals = $1,136.35       $1,235.1470   $1,235.14   $1,235.20   $1,235.20