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 $244.96   7.341%   $262.9425   $262.94   $262.95   $262.90  
  Purchase #2 $216.68   7.721%   $233.4099   $233.41   $233.40   $233.40  
  Purchase #3 $166.32   3.126%   $171.5192   $171.52   $171.50   $171.50  
  Purchase #4 $152.73   10.742%   $169.1363   $169.14   $169.15   $169.10  
  Purchase #5 $132.70   8.211%   $143.596   $143.60   $143.60   $143.60  
  Purchase #6 $238.79   3.127%   $246.257   $246.26   $246.25   $246.30  
  Purchase #7 $53.66   7.439%   $57.6518   $57.65   $57.65   $57.70  
  7 purchase totals = $1,205.84       $1,284.5127   $1,284.52   $1,284.50   $1,284.50