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 $180.59   8.832%   $196.5397   $196.54   $196.55   $196.50  
  Purchase #2 $205.89   11.196%   $228.9414   $228.94   $228.95   $228.90  
  Purchase #3 $224.61   10.282%   $247.7044   $247.70   $247.70   $247.70  
  Purchase #4 $124.58   4.175%   $129.7812   $129.78   $129.80   $129.80  
  Purchase #5 $205.92   8.504%   $223.4314   $223.43   $223.45   $223.40  
  Purchase #6 $193.96   8.553%   $210.5494   $210.55   $210.55   $210.50  
  Purchase #7 $12.26   13.856%   $13.9587   $13.96   $13.95   $14.00  
  7 purchase totals = $1,147.81       $1,250.9062   $1,250.90   $1,250.95   $1,250.80