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 $24.36   6.236%   $25.8791   $25.88   $25.90   $25.90  
  Purchase #2 $200.35   10.767%   $221.9217   $221.92   $221.90   $221.90  
  Purchase #3 $148.93   3.348%   $153.9162   $153.92   $153.90   $153.90  
  Purchase #4 $217.32   7.642%   $233.9276   $233.93   $233.95   $233.90  
  Purchase #5 $94.83   13.640%   $107.7648   $107.76   $107.75   $107.80  
  Purchase #6 $102.84   10.412%   $113.5477   $113.55   $113.55   $113.50  
  Purchase #7 $204.84   6.559%   $218.2755   $218.28   $218.30   $218.30  
  7 purchase totals = $993.47       $1,075.2326   $1,075.24   $1,075.25   $1,075.20