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 $56.30   6.104%   $59.7366   $59.74   $59.75   $59.70  
  Purchase #2 $218.78   7.794%   $235.8317   $235.83   $235.85   $235.80  
  Purchase #3 $84.64   3.416%   $87.5313   $87.53   $87.55   $87.50  
  Purchase #4 $228.30   11.110%   $253.6641   $253.66   $253.65   $253.70  
  Purchase #5 $186.62   6.800%   $199.3102   $199.31   $199.30   $199.30  
  Purchase #6 $101.27   3.535%   $104.8499   $104.85   $104.85   $104.80  
  Purchase #7 $104.26   9.330%   $113.9875   $113.99   $114.00   $114.00  
  7 purchase totals = $980.17       $1,054.9113   $1,054.91   $1,054.95   $1,054.80