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 $72.55   5.776%   $76.7405   $76.74   $76.75   $76.70  
  Purchase #2 $129.56   13.129%   $146.5699   $146.57   $146.55   $146.60  
  Purchase #3 $167.44   11.697%   $187.0255   $187.03   $187.05   $187.00  
  Purchase #4 $245.43   5.288%   $258.4083   $258.41   $258.40   $258.40  
  Purchase #5 $116.90   8.492%   $126.8271   $126.83   $126.85   $126.80  
  Purchase #6 $137.60   7.278%   $147.6145   $147.61   $147.60   $147.60  
  Purchase #7 $26.51   9.679%   $29.0759   $29.08   $29.10   $29.10  
  7 purchase totals = $895.99       $972.2617   $972.27   $972.30   $972.20