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 $59.31   11.786%   $66.3003   $66.30   $66.30   $66.30  
  Purchase #2 $144.70   12.369%   $162.5979   $162.60   $162.60   $162.60  
  Purchase #3 $109.93   10.652%   $121.6397   $121.64   $121.65   $121.60  
  Purchase #4 $143.48   6.428%   $152.7029   $152.70   $152.70   $152.70  
  Purchase #5 $171.61   11.229%   $190.8801   $190.88   $190.90   $190.90  
  Purchase #6 $201.50   13.764%   $229.2345   $229.23   $229.25   $229.20  
  Purchase #7 $211.78   8.724%   $230.2557   $230.26   $230.25   $230.30  
  7 purchase totals = $1,042.31       $1,153.6111   $1,153.61   $1,153.65   $1,153.60