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 $219.52   10.599%   $242.7869   $242.79   $242.80   $242.80  
  Purchase #2 $193.69   4.621%   $202.6404   $202.64   $202.65   $202.60  
  Purchase #3 $68.36   11.688%   $76.3499   $76.35   $76.35   $76.30  
  Purchase #4 $220.63   7.764%   $237.7597   $237.76   $237.75   $237.80  
  Purchase #5 $43.50   8.821%   $47.3371   $47.34   $47.35   $47.30  
  Purchase #6 $149.85   7.669%   $161.342   $161.34   $161.35   $161.30  
  Purchase #7 $47.64   13.870%   $54.2477   $54.25   $54.25   $54.20  
  7 purchase totals = $943.19       $1,022.4637   $1,022.47   $1,022.50   $1,022.30