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 $8.52   12.477%   $9.583   $9.58   $9.60   $9.60  
  Purchase #2 $100.60   12.328%   $113.002   $113.00   $113.00   $113.00  
  Purchase #3 $17.60   10.577%   $19.4616   $19.46   $19.45   $19.50  
  Purchase #4 $17.40   5.755%   $18.4014   $18.40   $18.40   $18.40  
  Purchase #5 $180.57   5.390%   $190.3027   $190.30   $190.30   $190.30  
  Purchase #6 $45.64   6.531%   $48.6207   $48.62   $48.60   $48.60  
  Purchase #7 $227.38   12.717%   $256.2959   $256.30   $256.30   $256.30  
  7 purchase totals = $597.71       $655.6673   $655.66   $655.65   $655.70