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 $88.81   10.416%   $98.0604   $98.06   $98.05   $98.10  
  Purchase #2 $202.40   9.717%   $222.0672   $222.07   $222.05   $222.10  
  Purchase #3 $248.73   9.571%   $272.5359   $272.54   $272.55   $272.50  
  Purchase #4 $87.28   12.113%   $97.8522   $97.85   $97.85   $97.90  
  Purchase #5 $157.81   9.828%   $173.3196   $173.32   $173.30   $173.30  
  Purchase #6 $182.71   8.411%   $198.0777   $198.08   $198.10   $198.10  
  Purchase #7 $184.26   10.104%   $202.8776   $202.88   $202.90   $202.90  
  7 purchase totals = $1,152.00       $1,264.7906   $1,264.80   $1,264.80   $1,264.90