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 $83.85   13.490%   $95.1614   $95.16   $95.15   $95.20  
  Purchase #2 $181.49   3.552%   $187.9365   $187.94   $187.95   $187.90  
  Purchase #3 $5.65   13.672%   $6.4225   $6.42   $6.40   $6.40  
  Purchase #4 $215.59   10.128%   $237.425   $237.43   $237.45   $237.40  
  Purchase #5 $115.51   12.321%   $129.742   $129.74   $129.75   $129.70  
  Purchase #6 $64.50   6.356%   $68.5996   $68.60   $68.60   $68.60  
  Purchase #7 $170.76   7.202%   $183.0581   $183.06   $183.05   $183.10  
  7 purchase totals = $837.35       $908.3451   $908.35   $908.35   $908.30