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 $57.90   8.813%   $63.0027   $63.00   $63.00   $63.00  
  Purchase #2 $241.88   12.718%   $272.6423   $272.64   $272.65   $272.60  
  Purchase #3 $152.49   9.562%   $167.0711   $167.07   $167.05   $167.10  
  Purchase #4 $60.82   12.591%   $68.4778   $68.48   $68.50   $68.50  
  Purchase #5 $76.84   4.362%   $80.1918   $80.19   $80.20   $80.20  
  Purchase #6 $192.83   8.462%   $209.1473   $209.15   $209.15   $209.10  
  Purchase #7 $44.64   11.478%   $49.7638   $49.76   $49.75   $49.80  
  7 purchase totals = $827.40       $910.2968   $910.29   $910.30   $910.30