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 $211.82   4.474%   $221.2968   $221.30   $221.30   $221.30  
  Purchase #2 $82.93   7.151%   $88.8603   $88.86   $88.85   $88.90  
  Purchase #3 $62.70   8.595%   $68.0891   $68.09   $68.10   $68.10  
  Purchase #4 $204.38   4.787%   $214.1637   $214.16   $214.15   $214.20  
  Purchase #5 $68.63   6.659%   $73.2001   $73.20   $73.20   $73.20  
  Purchase #6 $247.38   11.623%   $276.133   $276.13   $276.15   $276.10  
  Purchase #7 $120.70   12.509%   $135.7984   $135.80   $135.80   $135.80  
  7 purchase totals = $998.54       $1,077.5414   $1,077.54   $1,077.55   $1,077.60