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 $114.75   11.541%   $127.9933   $127.99   $128.00   $128.00  
  Purchase #2 $175.64   9.295%   $191.9657   $191.97   $191.95   $192.00  
  Purchase #3 $59.56   11.699%   $66.5279   $66.53   $66.55   $66.50  
  Purchase #4 $106.47   6.636%   $113.5353   $113.54   $113.55   $113.50  
  Purchase #5 $97.99   6.257%   $104.1212   $104.12   $104.10   $104.10  
  Purchase #6 $123.87   8.717%   $134.6677   $134.67   $134.65   $134.70  
  Purchase #7 $232.98   6.344%   $247.7603   $247.76   $247.75   $247.80  
  7 purchase totals = $911.26       $986.5714   $986.58   $986.55   $986.60