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 $167.85   9.629%   $184.0123   $184.01   $184.00   $184.00  
  Purchase #2 $239.80   4.166%   $249.7901   $249.79   $249.80   $249.80  
  Purchase #3 $138.35   6.670%   $147.5779   $147.58   $147.60   $147.60  
  Purchase #4 $232.92   5.807%   $246.4457   $246.45   $246.45   $246.40  
  Purchase #5 $228.71   11.335%   $254.6343   $254.63   $254.65   $254.60  
  Purchase #6 $122.93   13.589%   $139.635   $139.64   $139.65   $139.60  
  Purchase #7 $27.42   11.324%   $30.525   $30.53   $30.55   $30.50  
  7 purchase totals = $1,157.98       $1,252.6203   $1,252.63   $1,252.70   $1,252.50