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 $63.94   5.336%   $67.3518   $67.35   $67.35   $67.40  
  Purchase #2 $248.85   11.321%   $277.0223   $277.02   $277.00   $277.00  
  Purchase #3 $238.60   12.817%   $269.1814   $269.18   $269.20   $269.20  
  Purchase #4 $94.97   9.331%   $103.8317   $103.83   $103.85   $103.80  
  Purchase #5 $37.92   13.269%   $42.9516   $42.95   $42.95   $43.00  
  Purchase #6 $117.77   9.779%   $129.2867   $129.29   $129.30   $129.30  
  Purchase #7 $27.58   11.483%   $30.747   $30.75   $30.75   $30.70  
  7 purchase totals = $829.63       $920.3725   $920.37   $920.40   $920.40