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 $160.80   9.347%   $175.83   $175.83   $175.85   $175.80  
  Purchase #2 $22.41   11.391%   $24.9627   $24.96   $24.95   $25.00  
  Purchase #3 $68.38   11.719%   $76.3935   $76.39   $76.40   $76.40  
  Purchase #4 $250.87   7.190%   $268.9076   $268.91   $268.90   $268.90  
  Purchase #5 $52.29   4.614%   $54.7027   $54.70   $54.70   $54.70  
  Purchase #6 $67.74   13.729%   $77.04   $77.04   $77.05   $77.00  
  Purchase #7 $32.57   12.131%   $36.5211   $36.52   $36.50   $36.50  
  7 purchase totals = $655.06       $714.3576   $714.35   $714.35   $714.30