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 $206.92   4.401%   $216.0265   $216.03   $216.05   $216.00  
  Purchase #2 $43.43   13.397%   $49.2483   $49.25   $49.25   $49.20  
  Purchase #3 $204.40   3.854%   $212.2776   $212.28   $212.30   $212.30  
  Purchase #4 $98.26   7.761%   $105.886   $105.89   $105.90   $105.90  
  Purchase #5 $241.33   11.218%   $268.4024   $268.40   $268.40   $268.40  
  Purchase #6 $123.26   6.429%   $131.1844   $131.18   $131.20   $131.20  
  Purchase #7 $147.60   3.795%   $153.2014   $153.20   $153.20   $153.20  
  7 purchase totals = $1,065.20       $1,136.2266   $1,136.23   $1,136.30   $1,136.20