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 $24.93   9.640%   $27.3333   $27.33   $27.35   $27.30  
  Purchase #2 $126.57   6.148%   $134.3515   $134.35   $134.35   $134.40  
  Purchase #3 $54.28   3.261%   $56.0501   $56.05   $56.05   $56.10  
  Purchase #4 $117.69   6.446%   $125.2763   $125.28   $125.30   $125.30  
  Purchase #5 $46.65   13.479%   $52.938   $52.94   $52.95   $52.90  
  Purchase #6 $109.79   6.172%   $116.5662   $116.57   $116.55   $116.60  
  Purchase #7 $100.42   10.755%   $111.2202   $111.22   $111.20   $111.20  
  7 purchase totals = $580.33       $623.7356   $623.74   $623.75   $623.80