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 $212.54   6.851%   $227.1011   $227.10   $227.10   $227.10  
  Purchase #2 $197.29   13.335%   $223.5986   $223.60   $223.60   $223.60  
  Purchase #3 $120.55   5.313%   $126.9548   $126.95   $126.95   $127.00  
  Purchase #4 $59.26   8.601%   $64.357   $64.36   $64.35   $64.40  
  Purchase #5 $182.54   6.197%   $193.852   $193.85   $193.85   $193.90  
  Purchase #6 $93.96   3.679%   $97.4168   $97.42   $97.40   $97.40  
  Purchase #7 $63.71   7.522%   $68.5023   $68.50   $68.50   $68.50  
  7 purchase totals = $929.85       $1,001.7826   $1,001.78   $1,001.75   $1,001.90