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 $237.44   7.387%   $254.9797   $254.98   $255.00   $255.00  
  Purchase #2 $168.52   11.247%   $187.4734   $187.47   $187.45   $187.50  
  Purchase #3 $89.42   12.772%   $100.8407   $100.84   $100.85   $100.80  
  Purchase #4 $84.99   3.274%   $87.7726   $87.77   $87.75   $87.80  
  Purchase #5 $76.60   9.867%   $84.1581   $84.16   $84.15   $84.20  
  Purchase #6 $60.35   6.622%   $64.3464   $64.35   $64.35   $64.30  
  Purchase #7 $207.76   4.836%   $217.8073   $217.81   $217.80   $217.80  
  7 purchase totals = $925.08       $997.3782   $997.38   $997.35   $997.40