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 $242.76   9.368%   $265.5018   $265.50   $265.50   $265.50  
  Purchase #2 $203.39   4.819%   $213.1914   $213.19   $213.20   $213.20  
  Purchase #3 $173.29   12.587%   $195.102   $195.10   $195.10   $195.10  
  Purchase #4 $12.87   11.815%   $14.3906   $14.39   $14.40   $14.40  
  Purchase #5 $246.85   5.461%   $260.3305   $260.33   $260.35   $260.30  
  Purchase #6 $58.65   5.615%   $61.9432   $61.94   $61.95   $61.90  
  Purchase #7 $245.47   11.427%   $273.5199   $273.52   $273.50   $273.50  
  7 purchase totals = $1,183.28       $1,283.9794   $1,283.97   $1,284.00   $1,283.90