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 $71.46   11.145%   $79.4242   $79.42   $79.40   $79.40  
  Purchase #2 $208.35   13.106%   $235.6564   $235.66   $235.65   $235.70  
  Purchase #3 $45.50   11.133%   $50.5655   $50.57   $50.55   $50.60  
  Purchase #4 $76.32   12.404%   $85.7867   $85.79   $85.80   $85.80  
  Purchase #5 $200.55   7.661%   $215.9141   $215.91   $215.90   $215.90  
  Purchase #6 $202.38   10.845%   $224.3281   $224.33   $224.35   $224.30  
  Purchase #7 $148.88   12.220%   $167.0731   $167.07   $167.05   $167.10  
  7 purchase totals = $953.44       $1,058.7481   $1,058.75   $1,058.70   $1,058.80