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 $54.86   7.128%   $58.7704   $58.77   $58.75   $58.80  
  Purchase #2 $244.72   11.325%   $272.4345   $272.43   $272.45   $272.40  
  Purchase #3 $197.75   4.310%   $206.273   $206.27   $206.25   $206.30  
  Purchase #4 $95.37   12.684%   $107.4667   $107.47   $107.45   $107.50  
  Purchase #5 $231.90   11.641%   $258.8955   $258.90   $258.90   $258.90  
  Purchase #6 $175.39   7.847%   $189.1529   $189.15   $189.15   $189.20  
  Purchase #7 $235.43   11.523%   $262.5586   $262.56   $262.55   $262.60  
  7 purchase totals = $1,235.42       $1,355.5516   $1,355.55   $1,355.50   $1,355.70