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 $216.71   11.406%   $241.4279   $241.43   $241.45   $241.40  
  Purchase #2 $149.35   4.796%   $156.5128   $156.51   $156.50   $156.50  
  Purchase #3 $229.85   6.653%   $245.1419   $245.14   $245.15   $245.10  
  Purchase #4 $23.56   8.474%   $25.5565   $25.56   $25.55   $25.60  
  Purchase #5 $19.48   8.837%   $21.2014   $21.20   $21.20   $21.20  
  Purchase #6 $183.41   7.756%   $197.6353   $197.64   $197.65   $197.60  
  Purchase #7 $169.25   6.655%   $180.5136   $180.51   $180.50   $180.50  
  7 purchase totals = $991.61       $1,067.9894   $1,067.99   $1,068.00   $1,067.90