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 $95.94   11.325%   $106.8052   $106.81   $106.80   $106.80  
  Purchase #2 $96.97   4.699%   $101.5266   $101.53   $101.55   $101.50  
  Purchase #3 $8.93   10.773%   $9.892   $9.89   $9.90   $9.90  
  Purchase #4 $69.62   13.361%   $78.9219   $78.92   $78.90   $78.90  
  Purchase #5 $39.30   10.140%   $43.285   $43.29   $43.30   $43.30  
  Purchase #6 $209.54   4.182%   $218.303   $218.30   $218.30   $218.30  
  Purchase #7 $111.94   7.270%   $120.078   $120.08   $120.10   $120.10  
  7 purchase totals = $632.24       $678.8117   $678.82   $678.85   $678.80