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 $88.93   8.604%   $96.5815   $96.58   $96.60   $96.60  
  Purchase #2 $217.49   7.290%   $233.345   $233.35   $233.35   $233.30  
  Purchase #3 $217.26   4.215%   $226.4175   $226.42   $226.40   $226.40  
  Purchase #4 $230.73   7.665%   $248.4155   $248.42   $248.40   $248.40  
  Purchase #5 $194.88   5.181%   $204.9767   $204.98   $205.00   $205.00  
  Purchase #6 $87.76   5.630%   $92.7009   $92.70   $92.70   $92.70  
  Purchase #7 $206.83   6.686%   $220.6587   $220.66   $220.65   $220.70  
  7 purchase totals = $1,243.88       $1,323.0958   $1,323.11   $1,323.10   $1,323.10