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 $87.35   9.538%   $95.6814   $95.68   $95.70   $95.70  
  Purchase #2 $157.54   11.852%   $176.2116   $176.21   $176.20   $176.20  
  Purchase #3 $149.41   13.343%   $169.3458   $169.35   $169.35   $169.30  
  Purchase #4 $9.95   11.397%   $11.084   $11.08   $11.10   $11.10  
  Purchase #5 $86.98   10.871%   $96.4356   $96.44   $96.45   $96.40  
  Purchase #6 $89.72   11.211%   $99.7785   $99.78   $99.80   $99.80  
  Purchase #7 $22.44   9.820%   $24.6436   $24.64   $24.65   $24.60  
  7 purchase totals = $603.39       $673.1805   $673.18   $673.25   $673.10