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 $143.99   9.214%   $157.2572   $157.26   $157.25   $157.30  
  Purchase #2 $165.84   8.161%   $179.3742   $179.37   $179.35   $179.40  
  Purchase #3 $211.96   3.465%   $219.3044   $219.30   $219.30   $219.30  
  Purchase #4 $66.83   6.560%   $71.214   $71.21   $71.20   $71.20  
  Purchase #5 $141.45   8.283%   $153.1663   $153.17   $153.15   $153.20  
  Purchase #6 $53.43   6.457%   $56.88   $56.88   $56.90   $56.90  
  Purchase #7 $43.93   10.523%   $48.5528   $48.55   $48.55   $48.60  
  7 purchase totals = $827.43       $885.7489   $885.74   $885.70   $885.90