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 $95.52   8.815%   $103.9401   $103.94   $103.95   $103.90  
  Purchase #2 $192.53   9.556%   $210.9282   $210.93   $210.95   $210.90  
  Purchase #3 $221.48   3.240%   $228.656   $228.66   $228.65   $228.70  
  Purchase #4 $228.46   5.318%   $240.6095   $240.61   $240.60   $240.60  
  Purchase #5 $202.32   8.176%   $218.8617   $218.86   $218.85   $218.90  
  Purchase #6 $205.30   10.795%   $227.4621   $227.46   $227.45   $227.50  
  Purchase #7 $130.84   13.783%   $148.8737   $148.87   $148.85   $148.90  
  7 purchase totals = $1,276.45       $1,379.3313   $1,379.33   $1,379.30   $1,379.40