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 $61.87   10.603%   $68.4301   $68.43   $68.45   $68.40  
  Purchase #2 $81.84   10.486%   $90.4217   $90.42   $90.40   $90.40  
  Purchase #3 $186.55   6.502%   $198.6795   $198.68   $198.70   $198.70  
  Purchase #4 $73.47   12.734%   $82.8257   $82.83   $82.85   $82.80  
  Purchase #5 $231.95   6.731%   $247.5626   $247.56   $247.55   $247.60  
  Purchase #6 $243.34   8.119%   $263.0968   $263.10   $263.10   $263.10  
  Purchase #7 $83.93   11.525%   $93.6029   $93.60   $93.60   $93.60  
  7 purchase totals = $962.95       $1,044.6193   $1,044.62   $1,044.65   $1,044.60