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 $86.87   9.529%   $95.1478   $95.15   $95.15   $95.10  
  Purchase #2 $151.76   8.582%   $164.784   $164.78   $164.80   $164.80  
  Purchase #3 $225.90   12.832%   $254.8875   $254.89   $254.90   $254.90  
  Purchase #4 $191.70   4.638%   $200.591   $200.59   $200.60   $200.60  
  Purchase #5 $160.67   5.330%   $169.2337   $169.23   $169.25   $169.20  
  Purchase #6 $30.43   6.782%   $32.4938   $32.49   $32.50   $32.50  
  Purchase #7 $61.33   12.583%   $69.0472   $69.05   $69.05   $69.00  
  7 purchase totals = $908.66       $986.1850   $986.18   $986.25   $986.10