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 $56.29   10.503%   $62.2021   $62.20   $62.20   $62.20  
  Purchase #2 $168.57   5.162%   $177.2716   $177.27   $177.25   $177.30  
  Purchase #3 $145.57   9.739%   $159.7471   $159.75   $159.75   $159.70  
  Purchase #4 $76.70   10.494%   $84.7489   $84.75   $84.75   $84.70  
  Purchase #5 $168.96   7.119%   $180.9883   $180.99   $181.00   $181.00  
  Purchase #6 $155.45   13.136%   $175.8699   $175.87   $175.85   $175.90  
  Purchase #7 $110.51   10.839%   $122.4882   $122.49   $122.50   $122.50  
  7 purchase totals = $882.05       $963.3161   $963.32   $963.30   $963.30