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 $247.67   7.698%   $266.7356   $266.74   $266.75   $266.70  
  Purchase #2 $123.92   10.264%   $136.6391   $136.64   $136.65   $136.60  
  Purchase #3 $102.62   5.520%   $108.2846   $108.28   $108.30   $108.30  
  Purchase #4 $56.77   6.493%   $60.4561   $60.46   $60.45   $60.50  
  Purchase #5 $81.58   6.849%   $87.1674   $87.17   $87.15   $87.20  
  Purchase #6 $140.78   11.462%   $156.9162   $156.92   $156.90   $156.90  
  Purchase #7 $172.82   3.295%   $178.5144   $178.51   $178.50   $178.50  
  7 purchase totals = $926.16       $994.7134   $994.72   $994.70   $994.70