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 $176.60   6.113%   $187.3956   $187.40   $187.40   $187.40  
  Purchase #2 $58.35   7.354%   $62.6411   $62.64   $62.65   $62.60  
  Purchase #3 $58.84   9.538%   $64.4522   $64.45   $64.45   $64.50  
  Purchase #4 $163.51   8.722%   $177.7713   $177.77   $177.75   $177.80  
  Purchase #5 $88.64   10.283%   $97.7549   $97.75   $97.75   $97.80  
  Purchase #6 $98.34   6.395%   $104.6288   $104.63   $104.65   $104.60  
  Purchase #7 $120.40   11.525%   $134.2761   $134.28   $134.30   $134.30  
  7 purchase totals = $764.68       $828.9200   $828.92   $828.95   $829.00