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 $51.95   5.759%   $54.9418   $54.94   $54.95   $54.90  
  Purchase #2 $58.90   4.436%   $61.5128   $61.51   $61.50   $61.50  
  Purchase #3 $244.87   5.129%   $257.4294   $257.43   $257.45   $257.40  
  Purchase #4 $223.35   12.456%   $251.1705   $251.17   $251.15   $251.20  
  Purchase #5 $50.78   3.651%   $52.634   $52.63   $52.65   $52.60  
  Purchase #6 $95.49   12.786%   $107.6994   $107.70   $107.70   $107.70  
  Purchase #7 $212.73   8.119%   $230.0015   $230.00   $230.00   $230.00  
  7 purchase totals = $938.07       $1,015.3894   $1,015.38   $1,015.40   $1,015.30