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 $89.61   3.718%   $92.9417   $92.94   $92.95   $92.90  
  Purchase #2 $96.97   10.564%   $107.2139   $107.21   $107.20   $107.20  
  Purchase #3 $231.83   11.335%   $258.1079   $258.11   $258.10   $258.10  
  Purchase #4 $145.48   5.865%   $154.0124   $154.01   $154.00   $154.00  
  Purchase #5 $123.42   7.852%   $133.1109   $133.11   $133.10   $133.10  
  Purchase #6 $196.51   13.630%   $223.2943   $223.29   $223.30   $223.30  
  Purchase #7 $81.36   11.814%   $90.9719   $90.97   $90.95   $91.00  
  7 purchase totals = $965.18       $1,059.6530   $1,059.64   $1,059.60   $1,059.60