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 $151.86   10.745%   $168.1774   $168.18   $168.20   $168.20  
  Purchase #2 $52.27   9.252%   $57.106   $57.11   $57.10   $57.10  
  Purchase #3 $113.34   8.442%   $122.9082   $122.91   $122.90   $122.90  
  Purchase #4 $235.72   7.179%   $252.6423   $252.64   $252.65   $252.60  
  Purchase #5 $74.86   12.557%   $84.2602   $84.26   $84.25   $84.30  
  Purchase #6 $56.99   5.485%   $60.1159   $60.12   $60.10   $60.10  
  Purchase #7 $214.67   5.279%   $226.0024   $226.00   $226.00   $226.00  
  7 purchase totals = $899.71       $971.2124   $971.22   $971.20   $971.20