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 $132.98   6.585%   $141.7367   $141.74   $141.75   $141.70  
  Purchase #2 $227.52   10.438%   $251.2685   $251.27   $251.25   $251.30  
  Purchase #3 $58.48   4.857%   $61.3204   $61.32   $61.30   $61.30  
  Purchase #4 $82.68   4.414%   $86.3295   $86.33   $86.35   $86.30  
  Purchase #5 $184.52   8.165%   $199.5861   $199.59   $199.60   $199.60  
  Purchase #6 $246.31   3.413%   $254.7166   $254.72   $254.70   $254.70  
  Purchase #7 $248.82   5.433%   $262.3384   $262.34   $262.35   $262.30  
  7 purchase totals = $1,181.31       $1,257.2962   $1,257.31   $1,257.30   $1,257.20