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 $82.82   12.748%   $93.3779   $93.38   $93.40   $93.40  
  Purchase #2 $167.59   5.391%   $176.6248   $176.62   $176.60   $176.60  
  Purchase #3 $145.77   4.114%   $151.767   $151.77   $151.75   $151.80  
  Purchase #4 $44.55   3.266%   $46.005   $46.01   $46.00   $46.00  
  Purchase #5 $103.40   3.358%   $106.8722   $106.87   $106.85   $106.90  
  Purchase #6 $23.78   9.255%   $25.9808   $25.98   $26.00   $26.00  
  Purchase #7 $208.88   12.206%   $234.3759   $234.38   $234.40   $234.40  
  7 purchase totals = $776.79       $835.0036   $835.01   $835.00   $835.10