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 $229.64   7.813%   $247.5818   $247.58   $247.60   $247.60  
  Purchase #2 $104.62   10.397%   $115.4973   $115.50   $115.50   $115.50  
  Purchase #3 $210.83   5.842%   $223.1467   $223.15   $223.15   $223.10  
  Purchase #4 $161.94   8.675%   $175.9883   $175.99   $176.00   $176.00  
  Purchase #5 $105.90   7.231%   $113.5576   $113.56   $113.55   $113.60  
  Purchase #6 $151.49   10.461%   $167.3374   $167.34   $167.35   $167.30  
  Purchase #7 $11.56   9.562%   $12.6654   $12.67   $12.65   $12.70  
  7 purchase totals = $975.98       $1,055.7745   $1,055.79   $1,055.80   $1,055.80