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 $57.53   10.143%   $63.3653   $63.37   $63.35   $63.40  
  Purchase #2 $50.89   10.339%   $56.1515   $56.15   $56.15   $56.20  
  Purchase #3 $43.77   8.518%   $47.4983   $47.50   $47.50   $47.50  
  Purchase #4 $25.28   6.334%   $26.8812   $26.88   $26.90   $26.90  
  Purchase #5 $168.73   7.596%   $181.5467   $181.55   $181.55   $181.50  
  Purchase #6 $83.80   12.762%   $94.4946   $94.49   $94.50   $94.50  
  Purchase #7 $90.29   4.483%   $94.3377   $94.34   $94.35   $94.30  
  7 purchase totals = $520.29       $564.2753   $564.28   $564.30   $564.30