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 $60.64   12.574%   $68.2649   $68.26   $68.25   $68.30  
  Purchase #2 $212.58   13.750%   $241.8098   $241.81   $241.80   $241.80  
  Purchase #3 $61.79   8.710%   $67.1719   $67.17   $67.15   $67.20  
  Purchase #4 $100.27   10.488%   $110.7863   $110.79   $110.80   $110.80  
  Purchase #5 $120.73   7.797%   $130.1433   $130.14   $130.15   $130.10  
  Purchase #6 $61.32   9.656%   $67.2411   $67.24   $67.25   $67.20  
  Purchase #7 $240.82   11.765%   $269.1525   $269.15   $269.15   $269.20  
  7 purchase totals = $858.15       $954.5698   $954.56   $954.55   $954.60