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 $186.51   5.551%   $196.8632   $196.86   $196.85   $196.90  
  Purchase #2 $50.74   11.369%   $56.5086   $56.51   $56.50   $56.50  
  Purchase #3 $34.58   8.617%   $37.5598   $37.56   $37.55   $37.60  
  Purchase #4 $230.95   5.391%   $243.4005   $243.40   $243.40   $243.40  
  Purchase #5 $113.53   7.403%   $121.9346   $121.93   $121.95   $121.90  
  Purchase #6 $169.78   4.401%   $177.252   $177.25   $177.25   $177.30  
  Purchase #7 $77.86   8.350%   $84.3613   $84.36   $84.35   $84.40  
  7 purchase totals = $863.95       $917.8800   $917.87   $917.85   $918.00