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 $91.93   11.238%   $102.2611   $102.26   $102.25   $102.30  
  Purchase #2 $143.67   12.242%   $161.2581   $161.26   $161.25   $161.30  
  Purchase #3 $111.70   4.429%   $116.6472   $116.65   $116.65   $116.60  
  Purchase #4 $85.93   10.398%   $94.865   $94.87   $94.85   $94.90  
  Purchase #5 $250.52   8.215%   $271.1002   $271.10   $271.10   $271.10  
  Purchase #6 $59.93   9.491%   $65.618   $65.62   $65.60   $65.60  
  Purchase #7 $248.67   5.510%   $262.3717   $262.37   $262.35   $262.40  
  7 purchase totals = $992.35       $1,074.1213   $1,074.13   $1,074.05   $1,074.20