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 $182.58   12.835%   $206.0141   $206.01   $206.00   $206.00  
  Purchase #2 $95.96   11.656%   $107.1451   $107.15   $107.15   $107.10  
  Purchase #3 $79.95   7.307%   $85.7919   $85.79   $85.80   $85.80  
  Purchase #4 $124.46   4.509%   $130.0719   $130.07   $130.05   $130.10  
  Purchase #5 $184.35   13.629%   $209.4751   $209.48   $209.50   $209.50  
  Purchase #6 $176.36   12.217%   $197.9059   $197.91   $197.90   $197.90  
  Purchase #7 $88.85   8.420%   $96.3312   $96.33   $96.35   $96.30  
  7 purchase totals = $932.51       $1,032.7352   $1,032.74   $1,032.75   $1,032.70