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 $60.32   8.621%   $65.5202   $65.52   $65.50   $65.50  
  Purchase #2 $157.61   6.116%   $167.2494   $167.25   $167.25   $167.20  
  Purchase #3 $233.86   6.119%   $248.1699   $248.17   $248.15   $248.20  
  Purchase #4 $108.40   12.832%   $122.3099   $122.31   $122.30   $122.30  
  Purchase #5 $147.38   9.260%   $161.0274   $161.03   $161.05   $161.00  
  Purchase #6 $53.27   10.108%   $58.6545   $58.65   $58.65   $58.70  
  Purchase #7 $89.48   5.192%   $94.1258   $94.13   $94.15   $94.10  
  7 purchase totals = $850.32       $917.0571   $917.06   $917.05   $917.00