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 $74.34   13.432%   $84.3253   $84.33   $84.35   $84.30  
  Purchase #2 $221.75   13.285%   $251.2095   $251.21   $251.20   $251.20  
  Purchase #3 $48.36   7.626%   $52.0479   $52.05   $52.05   $52.00  
  Purchase #4 $167.56   11.737%   $187.2265   $187.23   $187.25   $187.20  
  Purchase #5 $61.79   5.297%   $65.063   $65.06   $65.05   $65.10  
  Purchase #6 $168.76   10.517%   $186.5085   $186.51   $186.50   $186.50  
  Purchase #7 $160.36   12.725%   $180.7658   $180.77   $180.75   $180.80  
  7 purchase totals = $902.92       $1,007.1465   $1,007.16   $1,007.15   $1,007.10