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 $58.96   13.531%   $66.9379   $66.94   $66.95   $66.90  
  Purchase #2 $70.31   7.852%   $75.8307   $75.83   $75.85   $75.80  
  Purchase #3 $70.55   11.621%   $78.7486   $78.75   $78.75   $78.70  
  Purchase #4 $195.74   5.861%   $207.2123   $207.21   $207.20   $207.20  
  Purchase #5 $64.59   12.716%   $72.8033   $72.80   $72.80   $72.80  
  Purchase #6 $43.88   5.278%   $46.196   $46.20   $46.20   $46.20  
  Purchase #7 $229.99   3.311%   $237.605   $237.61   $237.60   $237.60  
  7 purchase totals = $734.02       $785.3338   $785.34   $785.35   $785.20