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 $81.93   5.613%   $86.5287   $86.53   $86.55   $86.50  
  Purchase #2 $149.96   9.608%   $164.3682   $164.37   $164.35   $164.40  
  Purchase #3 $55.80   10.848%   $61.8532   $61.85   $61.85   $61.90  
  Purchase #4 $169.65   13.366%   $192.3254   $192.33   $192.35   $192.30  
  Purchase #5 $180.46   13.213%   $204.3042   $204.30   $204.30   $204.30  
  Purchase #6 $131.61   6.406%   $140.0409   $140.04   $140.05   $140.00  
  Purchase #7 $106.36   5.843%   $112.5746   $112.57   $112.55   $112.60  
  7 purchase totals = $875.77       $961.9952   $961.99   $962.00   $962.00