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 $66.55   3.428%   $68.8313   $68.83   $68.85   $68.80  
  Purchase #2 $51.26   13.154%   $58.0027   $58.00   $58.00   $58.00  
  Purchase #3 $20.71   6.392%   $22.0338   $22.03   $22.05   $22.00  
  Purchase #4 $119.89   4.194%   $124.9182   $124.92   $124.90   $124.90  
  Purchase #5 $223.98   11.864%   $250.553   $250.55   $250.55   $250.60  
  Purchase #6 $185.36   13.107%   $209.6551   $209.66   $209.65   $209.70  
  Purchase #7 $226.97   5.257%   $238.9018   $238.90   $238.90   $238.90  
  7 purchase totals = $894.72       $972.8959   $972.89   $972.90   $972.90