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 $96.40   5.196%   $101.4089   $101.41   $101.40   $101.40  
  Purchase #2 $218.30   10.665%   $241.5817   $241.58   $241.60   $241.60  
  Purchase #3 $45.59   12.520%   $51.2979   $51.30   $51.30   $51.30  
  Purchase #4 $154.78   12.425%   $174.0114   $174.01   $174.00   $174.00  
  Purchase #5 $132.39   6.639%   $141.1794   $141.18   $141.20   $141.20  
  Purchase #6 $71.39   12.473%   $80.2945   $80.29   $80.30   $80.30  
  Purchase #7 $193.89   4.272%   $202.173   $202.17   $202.15   $202.20  
  7 purchase totals = $912.74       $991.9468   $991.94   $991.95   $992.00