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 $153.80   6.103%   $163.1864   $163.19   $163.20   $163.20  
  Purchase #2 $183.44   13.637%   $208.4557   $208.46   $208.45   $208.50  
  Purchase #3 $33.31   7.695%   $35.8732   $35.87   $35.85   $35.90  
  Purchase #4 $54.70   7.270%   $58.6767   $58.68   $58.70   $58.70  
  Purchase #5 $167.92   8.541%   $182.262   $182.26   $182.25   $182.30  
  Purchase #6 $123.93   8.464%   $134.4194   $134.42   $134.40   $134.40  
  Purchase #7 $217.43   12.119%   $243.7803   $243.78   $243.80   $243.80  
  7 purchase totals = $934.53       $1,026.6537   $1,026.66   $1,026.65   $1,026.80