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 $239.61   6.226%   $254.5281   $254.53   $254.55   $254.50  
  Purchase #2 $250.99   7.244%   $269.1717   $269.17   $269.15   $269.20  
  Purchase #3 $51.70   7.261%   $55.4539   $55.45   $55.45   $55.50  
  Purchase #4 $147.66   3.581%   $152.9477   $152.95   $152.95   $152.90  
  Purchase #5 $209.96   4.395%   $219.1877   $219.19   $219.20   $219.20  
  Purchase #6 $176.80   5.234%   $186.0537   $186.05   $186.05   $186.10  
  Purchase #7 $224.66   3.716%   $233.0084   $233.01   $233.00   $233.00  
  7 purchase totals = $1,301.38       $1,370.3512   $1,370.35   $1,370.35   $1,370.40