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 $94.41   10.801%   $104.6072   $104.61   $104.60   $104.60  
  Purchase #2 $7.68   8.455%   $8.3293   $8.33   $8.35   $8.30  
  Purchase #3 $82.91   13.328%   $93.9602   $93.96   $93.95   $94.00  
  Purchase #4 $245.58   3.155%   $253.328   $253.33   $253.35   $253.30  
  Purchase #5 $137.70   11.725%   $153.8453   $153.85   $153.85   $153.80  
  Purchase #6 $157.48   5.664%   $166.3997   $166.40   $166.40   $166.40  
  Purchase #7 $174.84   9.593%   $191.6124   $191.61   $191.60   $191.60  
  7 purchase totals = $900.60       $972.0821   $972.09   $972.10   $972.00