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 $57.97   4.668%   $60.676   $60.68   $60.70   $60.70  
  Purchase #2 $158.48   12.170%   $177.767   $177.77   $177.75   $177.80  
  Purchase #3 $56.71   5.292%   $59.7111   $59.71   $59.70   $59.70  
  Purchase #4 $110.55   5.738%   $116.8934   $116.89   $116.90   $116.90  
  Purchase #5 $232.93   6.771%   $248.7017   $248.70   $248.70   $248.70  
  Purchase #6 $112.72   7.371%   $121.0286   $121.03   $121.05   $121.00  
  Purchase #7 $112.26   13.380%   $127.2804   $127.28   $127.30   $127.30  
  7 purchase totals = $841.62       $912.0582   $912.06   $912.10   $912.10