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 $208.66   5.852%   $220.8708   $220.87   $220.85   $220.90  
  Purchase #2 $127.35   5.571%   $134.4447   $134.44   $134.45   $134.40  
  Purchase #3 $200.95   6.844%   $214.703   $214.70   $214.70   $214.70  
  Purchase #4 $167.40   7.590%   $180.1057   $180.11   $180.10   $180.10  
  Purchase #5 $200.90   5.281%   $211.5095   $211.51   $211.50   $211.50  
  Purchase #6 $135.47   8.344%   $146.7736   $146.77   $146.75   $146.80  
  Purchase #7 $134.49   9.768%   $147.627   $147.63   $147.65   $147.60  
  7 purchase totals = $1,175.22       $1,256.0343   $1,256.03   $1,256.00   $1,256.00