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 $218.76   10.270%   $241.2267   $241.23   $241.25   $241.20  
  Purchase #2 $186.99   8.679%   $203.2189   $203.22   $203.20   $203.20  
  Purchase #3 $208.73   8.403%   $226.2696   $226.27   $226.25   $226.30  
  Purchase #4 $120.91   12.431%   $135.9403   $135.94   $135.95   $135.90  
  Purchase #5 $154.59   7.284%   $165.8503   $165.85   $165.85   $165.90  
  Purchase #6 $150.78   6.646%   $160.8008   $160.80   $160.80   $160.80  
  Purchase #7 $69.84   7.212%   $74.8769   $74.88   $74.90   $74.90  
  7 purchase totals = $1,110.60       $1,208.1835   $1,208.19   $1,208.20   $1,208.20