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 $112.53   10.109%   $123.9057   $123.91   $123.90   $123.90  
  Purchase #2 $169.59   10.133%   $186.7746   $186.77   $186.75   $186.80  
  Purchase #3 $245.46   12.861%   $277.0286   $277.03   $277.05   $277.00  
  Purchase #4 $247.98   10.694%   $274.499   $274.50   $274.50   $274.50  
  Purchase #5 $245.65   12.625%   $276.6633   $276.66   $276.65   $276.70  
  Purchase #6 $176.48   7.683%   $190.039   $190.04   $190.05   $190.00  
  Purchase #7 $64.94   13.260%   $73.551   $73.55   $73.55   $73.60  
  7 purchase totals = $1,262.63       $1,402.4612   $1,402.46   $1,402.45   $1,402.50