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 $201.86   7.539%   $217.0782   $217.08   $217.10   $217.10  
  Purchase #2 $65.82   6.681%   $70.2174   $70.22   $70.20   $70.20  
  Purchase #3 $232.95   11.585%   $259.9373   $259.94   $259.95   $259.90  
  Purchase #4 $172.82   10.680%   $191.2772   $191.28   $191.30   $191.30  
  Purchase #5 $88.34   5.821%   $93.4823   $93.48   $93.50   $93.50  
  Purchase #6 $250.67   7.293%   $268.9514   $268.95   $268.95   $269.00  
  Purchase #7 $5.80   4.185%   $6.0427   $6.04   $6.05   $6.00  
  7 purchase totals = $1,018.26       $1,106.9865   $1,106.99   $1,107.05   $1,107.00