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 $236.93   13.856%   $269.759   $269.76   $269.75   $269.80  
  Purchase #2 $55.95   11.250%   $62.2444   $62.24   $62.25   $62.20  
  Purchase #3 $46.36   7.228%   $49.7109   $49.71   $49.70   $49.70  
  Purchase #4 $202.82   6.683%   $216.3745   $216.37   $216.35   $216.40  
  Purchase #5 $140.93   6.409%   $149.9622   $149.96   $149.95   $150.00  
  Purchase #6 $238.76   8.814%   $259.8043   $259.80   $259.80   $259.80  
  Purchase #7 $45.33   3.428%   $46.8839   $46.88   $46.90   $46.90  
  7 purchase totals = $967.08       $1,054.7392   $1,054.72   $1,054.70   $1,054.80