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 $100.90   7.744%   $108.7137   $108.71   $108.70   $108.70  
  Purchase #2 $133.36   4.741%   $139.6826   $139.68   $139.70   $139.70  
  Purchase #3 $209.45   5.754%   $221.5018   $221.50   $221.50   $221.50  
  Purchase #4 $103.35   4.503%   $108.0039   $108.00   $108.00   $108.00  
  Purchase #5 $237.40   3.373%   $245.4075   $245.41   $245.40   $245.40  
  Purchase #6 $166.32   12.600%   $187.2763   $187.28   $187.30   $187.30  
  Purchase #7 $78.71   4.406%   $82.178   $82.18   $82.20   $82.20  
  7 purchase totals = $1,029.49       $1,092.7638   $1,092.76   $1,092.80   $1,092.80