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 $56.26   12.147%   $63.0939   $63.09   $63.10   $63.10  
  Purchase #2 $91.90   10.589%   $101.6313   $101.63   $101.65   $101.60  
  Purchase #3 $11.76   5.335%   $12.3874   $12.39   $12.40   $12.40  
  Purchase #4 $208.64   4.841%   $218.7403   $218.74   $218.75   $218.70  
  Purchase #5 $237.70   7.621%   $255.8151   $255.82   $255.80   $255.80  
  Purchase #6 $190.67   6.172%   $202.4382   $202.44   $202.45   $202.40  
  Purchase #7 $241.73   5.345%   $254.6505   $254.65   $254.65   $254.70  
  7 purchase totals = $1,038.66       $1,108.7567   $1,108.76   $1,108.80   $1,108.70