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 $211.26   13.277%   $239.309   $239.31   $239.30   $239.30  
  Purchase #2 $5.38   13.693%   $6.1167   $6.12   $6.10   $6.10  
  Purchase #3 $219.32   9.716%   $240.6291   $240.63   $240.65   $240.60  
  Purchase #4 $86.66   11.585%   $96.6996   $96.70   $96.70   $96.70  
  Purchase #5 $31.82   6.620%   $33.9265   $33.93   $33.95   $33.90  
  Purchase #6 $191.27   8.180%   $206.9159   $206.92   $206.90   $206.90  
  Purchase #7 $158.28   11.772%   $176.9127   $176.91   $176.90   $176.90  
  7 purchase totals = $903.99       $1,000.5095   $1,000.52   $1,000.50   $1,000.40