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 $140.49   8.608%   $152.5834   $152.58   $152.60   $152.60  
  Purchase #2 $74.32   7.425%   $79.8383   $79.84   $79.85   $79.80  
  Purchase #3 $216.55   4.700%   $226.7279   $226.73   $226.75   $226.70  
  Purchase #4 $76.47   13.147%   $86.5235   $86.52   $86.50   $86.50  
  Purchase #5 $230.70   12.651%   $259.8859   $259.89   $259.90   $259.90  
  Purchase #6 $41.76   7.119%   $44.7329   $44.73   $44.75   $44.70  
  Purchase #7 $102.92   7.855%   $111.0044   $111.00   $111.00   $111.00  
  7 purchase totals = $883.21       $961.2963   $961.29   $961.35   $961.20