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 $247.77   10.544%   $273.8949   $273.89   $273.90   $273.90  
  Purchase #2 $23.28   5.872%   $24.647   $24.65   $24.65   $24.60  
  Purchase #3 $90.65   3.356%   $93.6922   $93.69   $93.70   $93.70  
  Purchase #4 $43.98   12.863%   $49.6371   $49.64   $49.65   $49.60  
  Purchase #5 $149.90   7.802%   $161.5952   $161.60   $161.60   $161.60  
  Purchase #6 $172.86   4.867%   $181.2731   $181.27   $181.25   $181.30  
  Purchase #7 $237.54   10.817%   $263.2347   $263.23   $263.25   $263.20  
  7 purchase totals = $965.98       $1,047.9742   $1,047.97   $1,048.00   $1,047.90