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 $248.66   5.588%   $262.5551   $262.56   $262.55   $262.60  
  Purchase #2 $50.50   11.515%   $56.3151   $56.32   $56.30   $56.30  
  Purchase #3 $103.52   12.674%   $116.6401   $116.64   $116.65   $116.60  
  Purchase #4 $168.70   8.394%   $182.8607   $182.86   $182.85   $182.90  
  Purchase #5 $205.96   6.281%   $218.8963   $218.90   $218.90   $218.90  
  Purchase #6 $237.79   3.454%   $246.0033   $246.00   $246.00   $246.00  
  Purchase #7 $204.77   8.674%   $222.5317   $222.53   $222.55   $222.50  
  7 purchase totals = $1,219.90       $1,305.8023   $1,305.81   $1,305.80   $1,305.80