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 $167.75   3.671%   $173.9081   $173.91   $173.90   $173.90  
  Purchase #2 $92.99   4.178%   $96.8751   $96.88   $96.90   $96.90  
  Purchase #3 $102.32   11.652%   $114.2423   $114.24   $114.25   $114.20  
  Purchase #4 $247.96   13.226%   $280.7552   $280.76   $280.75   $280.80  
  Purchase #5 $24.84   6.821%   $26.5343   $26.53   $26.55   $26.50  
  Purchase #6 $160.80   13.661%   $182.7669   $182.77   $182.75   $182.80  
  Purchase #7 $198.55   6.273%   $211.005   $211.01   $211.00   $211.00  
  7 purchase totals = $995.21       $1,086.0869   $1,086.10   $1,086.10   $1,086.10