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 $246.89   5.676%   $260.9035   $260.90   $260.90   $260.90  
  Purchase #2 $59.78   11.680%   $66.7623   $66.76   $66.75   $66.80  
  Purchase #3 $197.47   6.837%   $210.971   $210.97   $210.95   $211.00  
  Purchase #4 $227.50   6.457%   $242.1897   $242.19   $242.20   $242.20  
  Purchase #5 $140.56   5.173%   $147.8312   $147.83   $147.85   $147.80  
  Purchase #6 $54.92   8.472%   $59.5728   $59.57   $59.55   $59.60  
  Purchase #7 $37.42   3.600%   $38.7671   $38.77   $38.75   $38.80  
  7 purchase totals = $964.54       $1,026.9976   $1,026.99   $1,026.95   $1,027.10