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 $223.58   10.643%   $247.3756   $247.38   $247.40   $247.40  
  Purchase #2 $165.52   9.320%   $180.9465   $180.95   $180.95   $180.90  
  Purchase #3 $69.95   5.483%   $73.7854   $73.79   $73.80   $73.80  
  Purchase #4 $107.63   3.211%   $111.086   $111.09   $111.10   $111.10  
  Purchase #5 $53.91   10.240%   $59.4304   $59.43   $59.45   $59.40  
  Purchase #6 $230.44   9.840%   $253.1153   $253.12   $253.10   $253.10  
  Purchase #7 $247.91   11.639%   $276.7642   $276.76   $276.75   $276.80  
  7 purchase totals = $1,098.94       $1,202.5034   $1,202.52   $1,202.55   $1,202.50