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 $130.33   6.109%   $138.2919   $138.29   $138.30   $138.30  
  Purchase #2 $177.50   10.622%   $196.3541   $196.35   $196.35   $196.40  
  Purchase #3 $46.77   13.804%   $53.2261   $53.23   $53.25   $53.20  
  Purchase #4 $167.25   7.254%   $179.3823   $179.38   $179.40   $179.40  
  Purchase #5 $119.66   3.645%   $124.0216   $124.02   $124.00   $124.00  
  Purchase #6 $120.69   7.267%   $129.4605   $129.46   $129.45   $129.50  
  Purchase #7 $190.70   6.167%   $202.4605   $202.46   $202.45   $202.50  
  7 purchase totals = $952.90       $1,023.1970   $1,023.19   $1,023.20   $1,023.30