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 $84.26   5.124%   $88.5775   $88.58   $88.60   $88.60  
  Purchase #2 $155.38   9.192%   $169.6625   $169.66   $169.65   $169.70  
  Purchase #3 $54.67   3.703%   $56.6944   $56.69   $56.70   $56.70  
  Purchase #4 $245.69   6.746%   $262.2642   $262.26   $262.25   $262.30  
  Purchase #5 $154.39   3.170%   $159.2842   $159.28   $159.30   $159.30  
  Purchase #6 $145.53   13.233%   $164.788   $164.79   $164.80   $164.80  
  Purchase #7 $58.57   12.178%   $65.7027   $65.70   $65.70   $65.70  
  7 purchase totals = $898.49       $966.9735   $966.96   $967.00   $967.10