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 $103.75   13.285%   $117.5332   $117.53   $117.55   $117.50  
  Purchase #2 $147.88   3.776%   $153.4639   $153.46   $153.45   $153.50  
  Purchase #3 $43.86   6.237%   $46.5955   $46.60   $46.60   $46.60  
  Purchase #4 $118.34   6.550%   $126.0913   $126.09   $126.10   $126.10  
  Purchase #5 $88.79   8.209%   $96.0788   $96.08   $96.10   $96.10  
  Purchase #6 $164.77   5.662%   $174.0993   $174.10   $174.10   $174.10  
  Purchase #7 $49.90   7.308%   $53.5467   $53.55   $53.55   $53.50  
  7 purchase totals = $717.29       $767.4087   $767.41   $767.45   $767.40