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 $212.31   8.478%   $230.3096   $230.31   $230.30   $230.30  
  Purchase #2 $51.26   10.311%   $56.5454   $56.55   $56.55   $56.50  
  Purchase #3 $249.43   3.818%   $258.9532   $258.95   $258.95   $259.00  
  Purchase #4 $58.73   8.576%   $63.7667   $63.77   $63.75   $63.80  
  Purchase #5 $99.38   9.299%   $108.6213   $108.62   $108.60   $108.60  
  Purchase #6 $233.61   12.778%   $263.4607   $263.46   $263.45   $263.50  
  Purchase #7 $61.80   8.181%   $66.8559   $66.86   $66.85   $66.90  
  7 purchase totals = $966.52       $1,048.5128   $1,048.52   $1,048.45   $1,048.60