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 $214.90   12.116%   $240.9373   $240.94   $240.95   $240.90  
  Purchase #2 $88.91   13.702%   $101.0924   $101.09   $101.10   $101.10  
  Purchase #3 $79.62   3.454%   $82.3701   $82.37   $82.35   $82.40  
  Purchase #4 $228.65   11.550%   $255.0591   $255.06   $255.05   $255.10  
  Purchase #5 $165.79   13.315%   $187.8649   $187.86   $187.85   $187.90  
  Purchase #6 $57.30   7.567%   $61.6359   $61.64   $61.65   $61.60  
  Purchase #7 $240.50   10.635%   $266.0772   $266.08   $266.10   $266.10  
  7 purchase totals = $1,075.67       $1,195.0369   $1,195.04   $1,195.05   $1,195.10