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 $69.45   11.810%   $77.652   $77.65   $77.65   $77.70  
  Purchase #2 $233.45   4.775%   $244.5972   $244.60   $244.60   $244.60  
  Purchase #3 $88.48   4.822%   $92.7465   $92.75   $92.75   $92.70  
  Purchase #4 $179.67   7.157%   $192.529   $192.53   $192.55   $192.50  
  Purchase #5 $86.89   3.395%   $89.8399   $89.84   $89.85   $89.80  
  Purchase #6 $244.31   9.526%   $267.583   $267.58   $267.60   $267.60  
  Purchase #7 $25.73   3.435%   $26.6138   $26.61   $26.60   $26.60  
  7 purchase totals = $927.98       $991.5614   $991.56   $991.60   $991.50