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 $244.73   5.288%   $257.6713   $257.67   $257.65   $257.70  
  Purchase #2 $26.55   12.544%   $29.8804   $29.88   $29.90   $29.90  
  Purchase #3 $154.92   12.384%   $174.1053   $174.11   $174.10   $174.10  
  Purchase #4 $159.61   6.224%   $169.5441   $169.54   $169.55   $169.50  
  Purchase #5 $191.50   10.577%   $211.755   $211.76   $211.75   $211.80  
  Purchase #6 $151.67   13.836%   $172.6551   $172.66   $172.65   $172.70  
  Purchase #7 $59.62   3.537%   $61.7288   $61.73   $61.75   $61.70  
  7 purchase totals = $988.60       $1,077.3400   $1,077.35   $1,077.35   $1,077.40