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 $221.50   11.469%   $246.9038   $246.90   $246.90   $246.90  
  Purchase #2 $80.30   5.464%   $84.6876   $84.69   $84.70   $84.70  
  Purchase #3 $140.26   12.223%   $157.404   $157.40   $157.40   $157.40  
  Purchase #4 $83.31   3.218%   $85.9909   $85.99   $86.00   $86.00  
  Purchase #5 $200.40   12.151%   $224.7506   $224.75   $224.75   $224.80  
  Purchase #6 $194.80   12.646%   $219.4344   $219.43   $219.45   $219.40  
  Purchase #7 $32.50   5.128%   $34.1666   $34.17   $34.15   $34.20  
  7 purchase totals = $953.07       $1,053.3379   $1,053.33   $1,053.35   $1,053.40