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 $54.46   6.747%   $58.1344   $58.13   $58.15   $58.10  
  Purchase #2 $231.94   6.836%   $247.7954   $247.80   $247.80   $247.80  
  Purchase #3 $71.76   9.673%   $78.7013   $78.70   $78.70   $78.70  
  Purchase #4 $224.49   10.565%   $248.2074   $248.21   $248.20   $248.20  
  Purchase #5 $46.52   4.514%   $48.6199   $48.62   $48.60   $48.60  
  Purchase #6 $170.83   6.644%   $182.1799   $182.18   $182.20   $182.20  
  Purchase #7 $212.41   13.676%   $241.4592   $241.46   $241.45   $241.50  
  7 purchase totals = $1,012.41       $1,105.0975   $1,105.10   $1,105.10   $1,105.10