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 $63.40   3.565%   $65.6602   $65.66   $65.65   $65.70  
  Purchase #2 $94.77   13.544%   $107.6056   $107.61   $107.60   $107.60  
  Purchase #3 $209.60   9.832%   $230.2079   $230.21   $230.20   $230.20  
  Purchase #4 $24.29   4.346%   $25.3456   $25.35   $25.35   $25.30  
  Purchase #5 $70.72   5.467%   $74.5863   $74.59   $74.60   $74.60  
  Purchase #6 $66.68   9.651%   $73.1153   $73.12   $73.10   $73.10  
  Purchase #7 $184.90   8.754%   $201.0861   $201.09   $201.10   $201.10  
  7 purchase totals = $714.36       $777.6070   $777.63   $777.60   $777.60