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 $177.80   5.251%   $187.1363   $187.14   $187.15   $187.10  
  Purchase #2 $122.55   5.461%   $129.2425   $129.24   $129.25   $129.20  
  Purchase #3 $179.35   4.669%   $187.7239   $187.72   $187.70   $187.70  
  Purchase #4 $151.77   13.287%   $171.9357   $171.94   $171.95   $171.90  
  Purchase #5 $16.36   7.255%   $17.5469   $17.55   $17.55   $17.50  
  Purchase #6 $127.50   7.562%   $137.1416   $137.14   $137.15   $137.10  
  Purchase #7 $145.71   10.530%   $161.0533   $161.05   $161.05   $161.10  
  7 purchase totals = $921.04       $991.7802   $991.78   $991.80   $991.60