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 $110.51   13.363%   $125.2775   $125.28   $125.30   $125.30  
  Purchase #2 $108.48   12.765%   $122.3275   $122.33   $122.35   $122.30  
  Purchase #3 $44.69   5.481%   $47.1395   $47.14   $47.15   $47.10  
  Purchase #4 $19.25   10.823%   $21.3334   $21.33   $21.35   $21.30  
  Purchase #5 $228.58   9.652%   $250.6425   $250.64   $250.65   $250.60  
  Purchase #6 $226.61   11.655%   $253.0214   $253.02   $253.00   $253.00  
  Purchase #7 $110.63   7.729%   $119.1806   $119.18   $119.20   $119.20  
  7 purchase totals = $848.75       $938.9224   $938.92   $939.00   $938.80