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 $180.39   6.773%   $192.6078   $192.61   $192.60   $192.60  
  Purchase #2 $126.33   8.133%   $136.6044   $136.60   $136.60   $136.60  
  Purchase #3 $69.77   7.432%   $74.9553   $74.96   $74.95   $75.00  
  Purchase #4 $105.56   11.293%   $117.4809   $117.48   $117.50   $117.50  
  Purchase #5 $94.53   7.710%   $101.8183   $101.82   $101.80   $101.80  
  Purchase #6 $12.81   5.642%   $13.5327   $13.53   $13.55   $13.50  
  Purchase #7 $177.92   6.821%   $190.0559   $190.06   $190.05   $190.10  
  7 purchase totals = $767.31       $827.0553   $827.06   $827.05   $827.10