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 $191.67   8.532%   $208.0233   $208.02   $208.00   $208.00  
  Purchase #2 $246.32   5.823%   $260.6632   $260.66   $260.65   $260.70  
  Purchase #3 $220.98   3.469%   $228.6458   $228.65   $228.65   $228.60  
  Purchase #4 $212.86   3.322%   $219.9312   $219.93   $219.95   $219.90  
  Purchase #5 $70.83   5.556%   $74.7653   $74.77   $74.75   $74.80  
  Purchase #6 $51.66   6.448%   $54.991   $54.99   $55.00   $55.00  
  Purchase #7 $181.88   3.863%   $188.906   $188.91   $188.90   $188.90  
  7 purchase totals = $1,176.20       $1,235.9258   $1,235.93   $1,235.90   $1,235.90