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 $144.85   11.565%   $161.6019   $161.60   $161.60   $161.60  
  Purchase #2 $53.96   12.103%   $60.4908   $60.49   $60.50   $60.50  
  Purchase #3 $104.59   12.600%   $117.7683   $117.77   $117.75   $117.80  
  Purchase #4 $151.29   6.354%   $160.903   $160.90   $160.90   $160.90  
  Purchase #5 $238.46   5.675%   $251.9926   $251.99   $252.00   $252.00  
  Purchase #6 $201.58   10.117%   $221.9738   $221.97   $221.95   $222.00  
  Purchase #7 $206.94   8.872%   $225.2997   $225.30   $225.30   $225.30  
  7 purchase totals = $1,101.67       $1,200.0301   $1,200.02   $1,200.00   $1,200.10