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 $92.95   12.231%   $104.3187   $104.32   $104.30   $104.30  
  Purchase #2 $159.87   13.811%   $181.9496   $181.95   $181.95   $181.90  
  Purchase #3 $171.58   5.715%   $181.3858   $181.39   $181.40   $181.40  
  Purchase #4 $142.99   9.765%   $156.953   $156.95   $156.95   $157.00  
  Purchase #5 $168.37   8.133%   $182.0635   $182.06   $182.05   $182.10  
  Purchase #6 $47.28   3.297%   $48.8388   $48.84   $48.85   $48.80  
  Purchase #7 $230.99   6.422%   $245.8242   $245.82   $245.80   $245.80  
  7 purchase totals = $1,014.03       $1,101.3336   $1,101.33   $1,101.30   $1,101.30