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 $212.94   10.411%   $235.1092   $235.11   $235.10   $235.10  
  Purchase #2 $181.54   12.358%   $203.9747   $203.97   $203.95   $204.00  
  Purchase #3 $42.63   8.856%   $46.4053   $46.41   $46.40   $46.40  
  Purchase #4 $38.59   12.858%   $43.5519   $43.55   $43.55   $43.60  
  Purchase #5 $59.67   11.663%   $66.6293   $66.63   $66.65   $66.60  
  Purchase #6 $68.86   3.236%   $71.0883   $71.09   $71.10   $71.10  
  Purchase #7 $92.67   12.522%   $104.2741   $104.27   $104.25   $104.30  
  7 purchase totals = $696.90       $771.0328   $771.03   $771.00   $771.10