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 $248.39   7.873%   $267.9457   $267.95   $267.95   $267.90  
  Purchase #2 $182.49   10.741%   $202.0913   $202.09   $202.10   $202.10  
  Purchase #3 $44.60   5.385%   $47.0017   $47.00   $47.00   $47.00  
  Purchase #4 $141.82   4.341%   $147.9764   $147.98   $148.00   $148.00  
  Purchase #5 $175.66   7.744%   $189.2631   $189.26   $189.25   $189.30  
  Purchase #6 $57.34   9.361%   $62.7076   $62.71   $62.70   $62.70  
  Purchase #7 $153.85   11.797%   $171.9997   $172.00   $172.00   $172.00  
  7 purchase totals = $1,004.15       $1,088.9855   $1,088.99   $1,089.00   $1,089.00