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 $213.94   3.240%   $220.8717   $220.87   $220.85   $220.90  
  Purchase #2 $202.98   7.672%   $218.5526   $218.55   $218.55   $218.60  
  Purchase #3 $236.27   9.177%   $257.9525   $257.95   $257.95   $258.00  
  Purchase #4 $146.46   6.542%   $156.0414   $156.04   $156.05   $156.00  
  Purchase #5 $126.25   11.608%   $140.9051   $140.91   $140.90   $140.90  
  Purchase #6 $17.93   9.643%   $19.659   $19.66   $19.65   $19.70  
  Purchase #7 $38.89   12.802%   $43.8687   $43.87   $43.85   $43.90  
  7 purchase totals = $982.72       $1,057.8510   $1,057.85   $1,057.80   $1,058.00