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 $48.62   7.579%   $52.3049   $52.30   $52.30   $52.30  
  Purchase #2 $210.60   5.408%   $221.9892   $221.99   $222.00   $222.00  
  Purchase #3 $97.35   8.427%   $105.5537   $105.55   $105.55   $105.60  
  Purchase #4 $174.57   6.611%   $186.1108   $186.11   $186.10   $186.10  
  Purchase #5 $234.92   12.152%   $263.4675   $263.47   $263.45   $263.50  
  Purchase #6 $155.44   4.793%   $162.8902   $162.89   $162.90   $162.90  
  Purchase #7 $79.55   9.496%   $87.1041   $87.10   $87.10   $87.10  
  7 purchase totals = $1,001.05       $1,079.4204   $1,079.41   $1,079.40   $1,079.50