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 $246.51   11.608%   $275.1249   $275.12   $275.10   $275.10  
  Purchase #2 $60.90   13.710%   $69.2494   $69.25   $69.25   $69.20  
  Purchase #3 $210.39   11.858%   $235.338   $235.34   $235.35   $235.30  
  Purchase #4 $166.44   10.260%   $183.5167   $183.52   $183.50   $183.50  
  Purchase #5 $121.72   9.873%   $133.7374   $133.74   $133.75   $133.70  
  Purchase #6 $216.71   5.615%   $228.8783   $228.88   $228.90   $228.90  
  Purchase #7 $237.94   8.322%   $257.7414   $257.74   $257.75   $257.70  
  7 purchase totals = $1,260.61       $1,383.5861   $1,383.59   $1,383.60   $1,383.40