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 $163.27   13.171%   $184.7743   $184.77   $184.75   $184.80  
  Purchase #2 $23.98   8.369%   $25.9869   $25.99   $26.00   $26.00  
  Purchase #3 $176.42   12.394%   $198.2855   $198.29   $198.30   $198.30  
  Purchase #4 $231.54   13.573%   $262.9669   $262.97   $262.95   $263.00  
  Purchase #5 $177.70   6.757%   $189.7072   $189.71   $189.70   $189.70  
  Purchase #6 $242.39   4.261%   $252.7182   $252.72   $252.70   $252.70  
  Purchase #7 $182.75   13.307%   $207.0685   $207.07   $207.05   $207.10  
  7 purchase totals = $1,198.05       $1,321.5075   $1,321.52   $1,321.45   $1,321.60