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 $61.50   12.536%   $69.2096   $69.21   $69.20   $69.20  
  Purchase #2 $221.94   6.145%   $235.5782   $235.58   $235.60   $235.60  
  Purchase #3 $19.44   12.149%   $21.8018   $21.80   $21.80   $21.80  
  Purchase #4 $75.25   3.309%   $77.74   $77.74   $77.75   $77.70  
  Purchase #5 $162.41   11.370%   $180.876   $180.88   $180.90   $180.90  
  Purchase #6 $229.64   9.414%   $251.2583   $251.26   $251.25   $251.30  
  Purchase #7 $247.74   12.614%   $278.9899   $278.99   $279.00   $279.00  
  7 purchase totals = $1,017.92       $1,115.4538   $1,115.46   $1,115.50   $1,115.50